Run results for: Custom Flatmap

Run details:

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/131.0.0.0 Safari/537.36

Browser: Chrome 131

Operating system: Windows

Device Platform: Desktop

Date tested: 14 days ago

Test name	Executions per second
Native JS flatMap	19179.4 Ops/sec
Custom flatMap	33402.6 Ops/sec
lodash flatmap	22233.7 Ops/sec

HTML Preparation code:


<script src='https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.21/lodash.min.js'></script>

Script Preparation code:

const locations = [
    {'county': 'Mid Glamorgan', 'town': 'Aberdare'},
    {'county': 'Aberdeenshire', 'town': 'Aberdeen'},
    {'county': 'Gwynedd', 'town': 'Aberdovey'},
    {'county': 'Gwent', 'town': 'Abergavenny'},
    {'county': 'Clwyd', 'town': 'Abergele'},
    {'county': 'Gwent', 'town': 'Abertillery'},
    {'county': 'Dyfed', 'town': 'Aberystwyth'},
    {'county': 'Oxfordshire', 'town': 'Abingdon'},
    {'county': 'Lancashire', 'town': 'Accrington'},
    {'county': 'Lanarkshire', 'town': 'Airdrie'},
    {'county': 'Warwickshire', 'town': 'Alcester'},
    {'county': 'Suffolk', 'town': 'Aldeburgh'},
    {'county': 'Cheshire', 'town': 'Alderley Edge'},
    {'county': 'Hampshire', 'town': 'Aldershot'},
    {'county': 'Derbyshire', 'town': 'Alfreton'},
    {'county': 'Ross-shire', 'town': 'Alness'},
    {'county': 'Northumberland', 'town': 'Alnwick'},
    {'county': 'Hampshire', 'town': 'Alresford'},
    {'county': 'Cumbria', 'town': 'Alston'},
    {'county': 'Hampshire', 'town': 'Alton'},
    {'county': 'Cheshire', 'town': 'Altrincham'},
    {'county': 'Cumbria', 'town': 'Ambleside'},
    {'county': 'Buckinghamshire', 'town': 'Amersham'},
    {'county': 'Wiltshire', 'town': 'Amesbury'},
    {'county': 'Carmarthenshire', 'town': 'Ammanford'},
    {'county': 'Hampshire', 'town': 'Andover'},
    {'county': 'Fife', 'town': 'Anstruther'},
    {'county': 'Co Antrim', 'town': 'Antrim'},
    {'county': 'Cumbria', 'town': 'Appleby-in-Westmorland'},
    {'county': 'Angus', 'town': 'Arbroath'},
    {'county': 'Ayrshire', 'town': 'Ardrossan'},
    {'county': 'Co Armagh', 'town': 'Armagh'},
    {'county': 'Gwynedd', 'town': 'Arthog'},
    {'county': 'West Sussex', 'town': 'Arundel'},
    {'county': 'Berkshire', 'town': 'Ascot'},
    {'county': 'Derbyshire', 'town': 'Ashbourne'},
    {'county': 'Devon', 'town': 'Ashburton'},
    {'county': 'Kent', 'town': 'Ashford'},
    {'county': 'Middlesex', 'town': 'Ashford'},
    {'county': 'Northumberland', 'town': 'Ashington'},
    {'county': 'Surrey', 'town': 'Ashtead'},
    {'county': 'Greater Manchester', 'town': 'Ashton-under-Lyne'},
    {'county': 'Norfolk', 'town': 'Attleborough'},
    {'county': 'Inverness-shire', 'town': 'Aviemore'},
    {'county': 'Devon', 'town': 'Axminster'},
    {'county': 'Buckinghamshire', 'town': 'Aylesbury'},
    {'county': 'Ayrshire', 'town': 'Ayr'},
    {'county': 'Gwynedd', 'town': 'Bala'},
    {'county': 'Hertfordshire', 'town': 'Baldock'},
    {'county': 'Argyll', 'town': 'Ballachulish'},
    {'county': 'Co Antrim', 'town': 'Ballycastle'},
    {'county': 'Co Antrim', 'town': 'Ballyclare'},
    {'county': 'Co Antrim', 'town': 'Ballymena'},
    {'county': 'Co Antrim', 'town': 'Ballymoney'},
    {'county': 'Northumberland', 'town': 'Bamburgh'},
    {'county': 'Devon', 'town': 'Bamstaple'},
    {'county': 'Co Down', 'town': 'Banbridge'},
    {'county': 'Oxfordshire', 'town': 'Banbury'},
    {'county': 'Kincardineshire', 'town': 'Banchory'},
    {'county': 'Aberdeenshire', 'town': 'Banff'},
    {'county': 'Co Down', 'town': 'Bangor'},
    {'county': 'Gwynedd', 'town': 'Bangor'},
    {'county': 'Surrey', 'town': 'Banstead'},
    {'county': 'Essex', 'town': 'Barking'},
    {'county': 'Gwynedd', 'town': 'Barmouth'},
    {'county': 'Co Durham', 'town': 'Barnard Castle'},
    {'county': 'Hertfordshire', 'town': 'Barnet'},
    {'county': 'South Yorkshire', 'town': 'Barnsley'},
    {'county': 'Devon', 'town': 'Barnstaple'},
    {'county': 'South Glamorgan', 'town': 'Barry'},
    {'county': 'Cumbria', 'town': 'Barrow-in Furness'},
    {'county': 'South Humberside', 'town': 'Barton-upon-Humber'},
    {'county': 'Essex', 'town': 'Basildon'},
    {'county': 'Hampshire', 'town': 'Basingstoke'},
    {'county': 'Avon', 'town': 'Bath'},
    {'county': 'West Lothian', 'town': 'Bathgate'},
    {'county': 'East Sussex', 'town': 'Battle'},
    {'county': 'Gwynedd', 'town': 'Beaumaris'},
    {'county': 'Suffolk', 'town': 'Beccles'},
    {'county': 'Kent', 'town': 'Beckenham'},
    {'county': 'North Yorkshire', 'town': 'Bedale'},
    {'county': 'Bedfordshire', 'town': 'Bedford'},
    {'county': 'Belfast', 'town': 'Belfast'},
    {'county': 'Kent', 'town': 'Belvedere'},
    {'county': 'Essex', 'town': 'Benneet'},
    {'county': 'Hertfordshire', 'town': 'Berkhamsted'},
    {'county': 'Northumberland', 'town': 'Berwick-on-Tweed'},
    {'county': 'Conwy', 'town': 'Betws-y-Coed'},
    {'county': 'North Humberside', 'town': 'Beverley'},
    {'county': 'Worcestershire', 'town': 'Bewdley'},
    {'county': 'East Sussex', 'town': 'Bexhill-on-Sea'},
    {'county': 'Oxfordshire', 'town': 'Bicester'},
    {'county': 'Devon', 'town': 'Bideford'},
    {'county': 'Lanarkshire', 'town': 'Biggar'},
    {'county': 'Bedfordshire', 'town': 'Biggleswade'},
    {'county': 'Essex', 'town': 'Billericay'},
    {'county': 'West Sussex', 'town': 'Billingshurst'},
    {'county': 'West Yorkshire', 'town': 'Bingley'},
    {'county': 'Merseyside', 'town': 'Birkenhead'},
    {'county': 'West Midlands', 'town': 'Birmingham'},
    {'county': 'Co Durham', 'town': 'Bishop Auckland'},
    {'county': 'Shropshire', 'town': 'Bishops Castle'},
    {'county': 'Hertfordshire', 'town': 'Bishop\'s Stortford'},
    {'county': 'Hampshire', 'town': 'Bishops Waltham'},
    {'county': 'Lancashire', 'town': 'Blackburn'},
    {'county': 'Lancashire', 'town': 'Blackpool'},
    {'county': 'Gwynedd', 'town': 'Blaenau Ffestiniog'},
    {'county': 'Perthshire', 'town': 'Blairgowrie'},
    {'county': 'Dorset', 'town': 'Blandford Forum'},
    {'county': 'Tyne & Wear', 'town': 'Blaydon-on-Tyne'},
    {'county': 'Cornwall', 'town': 'Bodmin'},
    {'county': 'West Sussex', 'town': 'Bognor Regis'},
    {'county': 'Tyne & Wear', 'town': 'Boldon Colliery'},
    {'county': 'Lancashire', 'town': 'Bolton'},
    {'county': 'Midlothian', 'town': 'Bonnyrigg'},
    {'county': 'Merseyside', 'town': 'Bootle'},
    {'county': 'Hampshire', 'town': 'Bordon'},
    {'county': 'Hertfordshire', 'town': 'Borehamwood'},
    {'county': 'Lincolnshire', 'town': 'Boston'},
    {'county': 'West Lothian', 'town': 'Botness'},
    {'county': 'Lincolnshire', 'town': 'Bourne'},
    {'county': 'Dorset', 'town': 'Bournemouth'},
    {'county': 'Northamptonshire', 'town': 'Brackley'},
    {'county': 'Berkshire', 'town': 'Bracknell'},
    {'county': 'West Yorkshire', 'town': 'Bradford'},
    {'county': 'Essex', 'town': 'Braintree'},
    {'county': 'Cumbria', 'town': 'Brampton'},
    {'county': 'Devon', 'town': 'Braunton'},
    {'county': 'Powys', 'town': 'Brecon'},
    {'county': 'Middlesex', 'town': 'Brentford'},
    {'county': 'Essex', 'town': 'Brentwood'},
    {'county': 'Mid Glamorgan', 'town': 'Bridgend'},
    {'county': 'Shropshire', 'town': 'Bridgnorth'},
    {'county': 'Somerset', 'town': 'Bridgwater'},
    {'county': 'North Humberside', 'town': 'Bridlington'},
    {'county': 'Dorset', 'town': 'Bridport'},
    {'county': 'Lincolnshire', 'town': 'Brigg'},
    {'county': 'West Yorkshire', 'town': 'Brighouse'},
    {'county': 'East Sussex', 'town': 'Brighton'},
    {'county': 'Avon', 'town': 'Bristol'},
    {'county': 'Devon', 'town': 'Brixham'},
    {'county': 'Isle of Skye', 'town': 'Broadford'},
    {'county': 'Kent', 'town': 'Broadstairs'},
    {'county': 'Hereford & Worcester', 'town': 'Broadway'},
    {'county': 'Hampshire', 'town': 'Brockenhurst'},
    {'county': 'Isle of Arran', 'town': 'Brodick'},
    {'county': 'Kent', 'town': 'Bromley'},
    {'county': 'Hereford & Worcester', 'town': 'Bromsgrove'},
    {'county': 'Norfolk', 'town': 'Brooke'},
    {'county': 'West Lothian', 'town': 'Broxburn'},
    {'county': 'Devon', 'town': 'Buckfastleigh'},
    {'county': 'Essex', 'town': 'Buckhurst Hill'},
    {'county': 'Banffshire', 'town': 'Buckie'},
    {'county': 'Buckinghamshire', 'town': 'Buckingham'},
    {'county': 'Cornwall', 'town': 'Bude'},
    {'county': 'Devon', 'town': 'Budleigh Salterton'},
    {'county': 'Powys', 'town': 'Builth Wells'},
    {'county': 'Isle of Mull', 'town': 'Bunessan'},
    {'county': 'Suffolk', 'town': 'Bungay'},
    {'county': 'West Sussex', 'town': 'Burgess Hill'},
    {'county': 'Somerset', 'town': 'Burnham-on-Sea'},
    {'county': 'Lancashire', 'town': 'Burnley'},
    {'county': 'Staffordshire', 'town': 'Burton-on-Trent'},
    {'county': 'Lancashire', 'town': 'Bury'},
    {'county': 'Suffolk', 'town': 'Bury St Edmunds'},
    {'county': 'Co Antrim', 'town': 'Bushmills'},
    {'county': 'Derbyshire', 'town': 'Buxton'},
    {'county': 'Gwynedd', 'town': 'Caernarvon'},
    {'county': 'Mid Glamorgan', 'town': 'Caerphilly'},
    {'county': 'Wiltshire', 'town': 'Calne'},
    {'county': 'Surrey', 'town': 'Camberley'},
    {'county': 'Cambridgeshire', 'town': 'Cambridge'},
    {'county': 'Cornwall', 'town': 'Camelford'},
    {'county': 'Argyll', 'town': 'Campbeltown'},
    {'county': 'Staffordshire', 'town': 'Cannock'},
    {'county': 'Kent', 'town': 'Canterbury'},
    {'county': 'South Glamorgan', 'town': 'Cardiff'},
    {'county': 'Dyfed', 'town': 'Cardigan'},
    {'county': 'Cumbria', 'town': 'Carlisle'},
    {'county': 'Isle of Lewis', 'town': 'Carloway'},
    {'county': 'Lanarkshire', 'town': 'Carluke'},
    {'county': 'Dyfed', 'town': 'Carmarthen'},
    {'county': 'Lancashire', 'town': 'Carnforth'},
    {'county': 'Co Antrim', 'town': 'Carrickfergus'},
    {'county': 'Surrey', 'town': 'Carshalton'},
    {'county': 'Kirkcudbrightshire', 'town': 'Castle Douglas'},
    {'county': 'Co Tyrone', 'town': 'Castlederg'},
    {'county': 'Isle of Man', 'town': 'Castletown'},
    {'county': 'Co Down', 'town': 'Castlewellan'},
    {'county': 'Surrey', 'town': 'Caterham'},
    {'county': 'Gwynedd', 'town': 'Cemmaes Bay'},
    {'county': 'Gwynedd', 'town': 'Cemmaes Road'},
    {'county': 'Dorset', 'town': 'Cerne Abbas'},
    {'county': 'Somerset', 'town': 'Chard'},
    {'county': 'Kent', 'town': 'Chatham'},
    {'county': 'Cambridgeshire', 'town': 'Chatteris'},
    {'county': 'Cheshire', 'town': 'Cheadle'},
    {'county': 'Surrey', 'town': 'Cheam'},
    {'county': 'Somerset', 'town': 'Cheddar'},
    {'county': 'Essex', 'town': 'Chelmsford'},
    {'county': 'Gloucestershire', 'town': 'Cheltenham'},
    {'county': 'Gwent', 'town': 'Chepstow'},
    {'county': 'Surrey', 'town': 'Chertsey'},
    {'county': 'Buckinghamshire', 'town': 'Chesham'},
    {'county': 'Cheshire', 'town': 'Chester'},
    {'county': 'Co Durham', 'town': 'Chester-le-Street'},
    {'county': 'Derbyshire', 'town': 'Chesterfield'},
    {'county': 'West Sussex', 'town': 'Chichester'},
    {'county': 'Wiltshire', 'town': 'Chippenham'},
    {'county': 'Oxfordshire', 'town': 'Chipping Norton'},
    {'county': 'Gloucestershire', 'town': 'Chipping Sodbury'},
    {'county': 'Lancashire', 'town': 'Chorley'},
    {'county': 'Dorset', 'town': 'Christchurch'},
    {'county': 'Shropshire', 'town': 'Church Stretton'},
    {'county': 'Gloucestershne', 'town': 'Cinderford'},
    {'county': 'Gloucestershire', 'town': 'Cirencester'},
    {'county': 'Essex', 'town': 'Clacton-on-Sea'},
    {'county': 'South Humberside', 'town': 'Cleethorpes'},
    {'county': 'Avon', 'town': 'Clevedon'},
    {'county': 'Lancashire', 'town': 'Clitheroe'},
    {'county': 'Co Tyrone', 'town': 'Clogher'},
    {'county': 'Northamptonshire', 'town': 'Clopton'},
    {'county': 'Leicestershire', 'town': 'Coalville'},
    {'county': 'Lanarkshire', 'town': 'Coatbridge'},
    {'county': 'Surrey', 'town': 'Cobham'},
    {'county': 'Cumbria', 'town': 'Cockermouth'},
    {'county': 'Essex', 'town': 'Colchester'},
    {'county': 'Warwickshire', 'town': 'Coleshill'},
    {'county': 'Co Londonderry', 'town': 'Coleraine'},
    {'county': 'Clwyd', 'town': 'Colwyn Bay'},
    {'county': 'Cheshire', 'town': 'Congleton'},
    {'county': 'Cumbria', 'town': 'Coniston'},
    {'county': 'Co Durham', 'town': 'Consett'},
    {'county': 'Gwynedd', 'town': 'Conwy'},
    {'county': 'Co Tyrone', 'town': 'Cookstown'},
    {'county': 'Lancashire', 'town': 'Coppull'},
    {'county': 'Northumberland', 'town': 'Corbridge'},
    {'county': 'Northamptonshire', 'town': 'Corby'},
    {'county': 'Clwyd', 'town': 'Corwen'},
    {'county': 'Surrey', 'town': 'Coulsdon'},
    {'county': 'West Midlands', 'town': 'Coventry'},
    {'county': 'Co Armagh', 'town': 'Craigavon'},
    {'county': 'Northumberland', 'town': 'Cramlington'},
    {'county': 'Kent', 'town': 'Cranbrook'},
    {'county': 'Surrey', 'town': 'Cranleigh'},
    {'county': 'Shropshire', 'town': 'Craven Arms'},
    {'county': 'West Sussex', 'town': 'Crawley'},
    {'county': 'Devon', 'town': 'Crediton'},
    {'county': 'Cheshire', 'town': 'Crewe'},
    {'county': 'Perthshire', 'town': 'Crieff'},
    {'county': 'Norfolk', 'town': 'Cromer'},
    {'county': 'East Sussex', 'town': 'Crowborough'},
    {'county': 'Inverness-shire', 'town': 'Croy'},
    {'county': 'Surrey', 'town': 'Croydon'},
    {'county': 'Co Antrim', 'town': 'Crumlin'},
    {'county': 'Devon', 'town': 'Cullompton'},
    {'county': 'East Ayrshire', 'town': 'Cumnock'},
    {'county': 'Fife', 'town': 'Cupar'},
    {'county': 'Gwent', 'town': 'Cwmbran'},
    {'county': 'Essex', 'town': 'Dagenham'},
    {'county': 'Kirkcudbrightshire', 'town': 'Dalbeattie'},
    {'county': 'Argyll', 'town': 'Dalmally'},
    {'county': 'Ayrshire', 'town': 'Dalry'},
    {'county': 'Co Durham', 'town': 'Darlington'},
    {'county': 'Kent', 'town': 'Dartford'},
    {'county': 'Ayrshire', 'town': 'Darvel'},
    {'county': 'Northamptonshire', 'town': 'Daventry'},
    {'county': 'Kent', 'town': 'Deal'},
    {'county': 'Clwyd', 'town': 'Deeside'},
    {'county': 'Derbyshire', 'town': 'Derby'},
    {'county': 'Norfolk', 'town': 'Dereham'},
    {'county': 'Wiltshire', 'town': 'Devizes'},
    {'county': 'West Yorkshire', 'town': 'Dewsbury'},
    {'county': 'Oxfordshire', 'town': 'Didcot'},
    {'county': 'South Glamorgan', 'town': 'Dinas Powis'},
    {'county': 'Ross-shire', 'town': 'Dingwall'},
    {'county': 'Norfolk', 'town': 'Diss'},
    {'county': 'Gwynedd', 'town': 'Dolgellau'},
    {'county': 'South Yorkshire', 'town': 'Doncaster'},
    {'county': 'Dorset', 'town': 'Dorchester'},
    {'county': 'Surrey', 'town': 'Dorking'},
    {'county': 'Sutherland', 'town': 'Dornoch'},
    {'county': 'Isle of Man', 'town': 'Douglas'},
    {'county': 'Kent', 'town': 'Dover'},
    {'county': 'Norfolk', 'town': 'Downham Market'},
    {'county': 'Co Down', 'town': 'Downpatrick'},
    {'county': 'North Humberside', 'town': 'Driffield'},
    {'county': 'Hereford & Worcester', 'town': 'Droitwich'},
    {'county': 'Co Down', 'town': 'Dromore'},
    {'county': 'West Midlands', 'town': 'Dudley'},
    {'county': 'Somerset', 'town': 'Dulverton'},
    {'county': 'Dunbartonshire', 'town': 'Dumbarton'},
    {'county': 'Dumfriesshire', 'town': 'Dumfries'},
    {'county': 'East Lothian', 'town': 'Dunbar'},
    {'county': 'Perthshire', 'town': 'Dunblane'},
    {'county': 'Angus', 'town': 'Dundee'},
    {'county': 'Fife', 'town': 'Dunfermline'},
    {'county': 'Co Tyrone', 'town': 'Dungannon'},
    {'county': 'Perthshire', 'town': 'Dunkeld'},
    {'county': 'Essex', 'town': 'Dunmow'},
    {'county': 'Belfast', 'town': 'Dunmurry'},
    {'county': 'Argyll', 'town': 'Dunoon'},
    {'county': 'Berwickshire', 'town': 'Duns'},
    {'county': 'Bedfordshire', 'town': 'Dunstable'},
    {'county': 'Co Durham', 'town': 'Durham'},
    {'county': 'Gloucestershire', 'town': 'Dursley'},
    {'county': 'North Yorkshire', 'town': 'Easingwold'},
    {'county': 'West Sussex', 'town': 'East Grinstead'},
    {'county': 'South Lanarkshire', 'town': 'East Kilbride'},
    {'county': 'Surrey', 'town': 'East Molesey'},
    {'county': 'East Sussex', 'town': 'Eastbourne'},
    {'county': 'Hampshire', 'town': 'Eastleigh'},
    {'county': 'Kent', 'town': 'Ebbsfleet'},
    {'county': 'Gwent', 'town': 'Ebbw Vale'},
    {'county': 'Kent', 'town': 'Edenbridge'},
    {'county': 'Middlesex', 'town': 'Edgware'},
    {'county': 'Edinburgh', 'town': 'Edinburgh'},
    {'county': 'Surrey', 'town': 'Egham'},
    {'county': 'Morayshire', 'town': 'Elgin'},
    {'county': 'Cheshire', 'town': 'Ellesmere Port'},
    {'county': 'Aberdeenshire', 'town': 'Ellon'},
    {'county': 'Cambridgeshire', 'town': 'Ely'},
    {'county': 'Hampshire', 'town': 'Emsworth'},
    {'county': 'Middlesex', 'town': 'Enfeld'},
    {'county': 'Co Fermanagh', 'town': 'Enniskillen'},
    {'county': 'Essex', 'town': 'Epping'},
    {'county': 'Surrey', 'town': 'Epsom'},
    {'county': 'Kent', 'town': 'Erith'},
    {'county': 'Surrey', 'town': 'Esher'},
    {'county': 'Worcestershire', 'town': 'Evesham'},
    {'county': 'Devon', 'town': 'Exeter'},
    {'county': 'Devon', 'town': 'Exmouth'},
    {'county': 'Norfolk', 'town': 'Fakenham'},
    {'county': 'Stirlingshire', 'town': 'Falkirk'},
    {'county': 'Cornwall', 'town': 'Falmouth'},
    {'county': 'Hampshire', 'town': 'Fareham'},
    {'county': 'Oxfordshire', 'town': 'Faringdon'},
    {'county': 'Hampshire', 'town': 'Farnborough'},
    {'county': 'Surrey', 'town': 'Farnham'},
    {'county': 'Suffolk', 'town': 'Felixstowe'},
    {'county': 'Dyfed', 'town': 'Fishguard'},
    {'county': 'Co Tyrone', 'town': 'Fivemiletown'},
    {'county': 'Hampshire', 'town': 'Fleet'},
    {'county': 'Lancashire', 'town': 'Fleetwood'},
    {'county': 'Clwyd', 'town': 'Flint'},
    {'county': 'Kent', 'town': 'Folkestone'},
    {'county': 'Angus', 'town': 'Forfar'},
    {'county': 'Inverness-shire', 'town': 'Fort William'},
    {'county': 'Ross-shire', 'town': 'Fortrose'},
    {'county': 'Cornwall', 'town': 'Fowey'},
    {'county': 'Aberdeenshire', 'town': 'Fraserburgh'},
    {'county': 'Isle of Wight', 'town': 'Freshwater'},
    {'county': 'Essex', 'town': 'Frinton-on-Sea'},
    {'county': 'Somerset', 'town': 'Frome'},
    {'county': 'Lincolnshire', 'town': 'Gainsborough'},
    {'county': 'Ross-shire', 'town': 'Gairloch'},
    {'county': 'Selkirkshire', 'town': 'Galasheils'},
    {'county': 'Lancashire', 'town': 'Garstang'},
    {'county': 'Tyne & Wear', 'town': 'Gateshead'},
    {'county': 'Buckinghamshire', 'town': 'Gerrards Cross'},
    {'county': 'Dorset', 'town': 'Gillingham'},
    {'county': 'Kent', 'town': 'Gillingham'},
    {'county': 'South Ayrshire', 'town': 'Girvan'},
    {'county': 'Rotherham', 'town': 'Glamorgan'},
    {'county': 'Glasgow', 'town': 'Glasgow'},
    {'county': 'Somerset', 'town': 'Glastonbury'},
    {'county': 'Fife', 'town': 'Glenrothes'},
    {'county': 'Derbyshire', 'town': 'Glossop'},
    {'county': 'Gloucestershire', 'town': 'Gloucester'},
    {'county': 'Surrey', 'town': 'Godalming'},
    {'county': 'Surrey', 'town': 'Godstone'},
    {'county': 'East Riding of Yorkshire', 'town': 'Goole'},
    {'county': 'Cumbria', 'town': 'Gosforth'},
    {'county': 'Hampshire', 'town': 'Gosport'},
    {'county': 'Cumbria', 'town': 'Grange-over-Sands'},
    {'county': 'Midlothian', 'town': 'Grangemouth'},
    {'county': 'Lincolnshire', 'town': 'Grantham'},
    {'county': 'Kent', 'town': 'Gravesend'},
    {'county': 'Essex', 'town': 'Grays Thurrock'},
    {'county': 'Essex', 'town': 'Great Dunmow'},
    {'county': 'Buckinghamshire', 'town': 'Great Missenden'},
    {'county': 'Norfolk', 'town': 'Great Yarmouth'},
    {'county': 'Middlesex', 'town': 'Greenford'},
    {'county': 'Renfrewshire', 'town': 'Greenock'},
    {'county': 'Dumfriesshire', 'town': 'Gretna'},
    {'county': 'South Humberside', 'town': 'Grimsby'},
    {'county': 'Channel Islands', 'town': 'Guernsey'},
    {'county': 'Surrey', 'town': 'Guildford'},
    {'county': 'North Yorkshire', 'town': 'Guisborough'},
    {'county': 'West Yorkshire', 'town': 'Guiseley'},
    {'county': 'East Lothian', 'town': 'Gullane'},
    {'county': 'Lanark shire', 'town': 'Hamilton'},
    {'county': 'East Lothian', 'town': 'Haddington'},
    {'county': 'East Sussex', 'town': 'Hailsham'},
    {'county': 'West Midlands', 'town': 'Halesowen'},
    {'county': 'West Yorkshire', 'town': 'Halifax'},
    {'county': 'Essex', 'town': 'Halstead'},
    {'county': 'Northumberland', 'town': 'Haltwhistle'},
    {'county': 'Middlesex', 'town': 'Hampton'},
    {'county': 'Essex', 'town': 'Harlow'},
    {'county': 'Hertfordshire', 'town': 'Harpenden'},
    {'county': 'North Yorkshire', 'town': 'Harrogate'},
    {'county': 'Middlesex', 'town': 'Harrow'},
    {'county': 'Cleveland', 'town': 'Hartlepool'},
    {'county': 'Essex', 'town': 'Harwich'},
    {'county': 'Surrey', 'town': 'Haslemere'},
    {'county': 'West Sussex', 'town': 'Hassocks'},
    {'county': 'East Sussex', 'town': 'Hastings'},
    {'county': 'Hertfordshire', 'town': 'Hatfield'},
    {'county': 'Derbyshire', 'town': 'Hathersage'},
    {'county': 'Hampshire', 'town': 'Havant'},
    {'county': 'Pembrokeshire', 'town': 'Haverfordwest'},
    {'county': 'Suffolk', 'town': 'Haverhill'},
    {'county': 'Roxburghshire', 'town': 'Hawick'},
    {'county': 'Cumbria', 'town': 'Hawkshead'},
    {'county': 'Powys', 'town': 'Hay-on-Wye'},
    {'county': 'Middlesex', 'town': 'Hayes'},
    {'county': 'Hampshire', 'town': 'Hayling Island'},
    {'county': 'West Sussex', 'town': 'Haywards Heath'},
    {'county': 'Derbyshire', 'town': 'Heanor'},
    {'county': 'East Sussex', 'town': 'Heathfield'},
    {'county': 'West Yorkshire', 'town': 'Hebden Bridge'},
    {'county': 'Dunbartonshire', 'town': 'Helensburgh'},
    {'county': 'North Yorkshire', 'town': 'Helmsley'},
    {'county': 'Cornwall', 'town': 'Helston'},
    {'county': 'Hertfordshire', 'town': 'Hemel Hempstead'},
    {'county': 'West Sussex', 'town': 'Henfield'},
    {'county': 'Oxfordshire', 'town': 'Henley-on-Thames'},
    {'county': 'Hereford & Worcester', 'town': 'Hereford'},
    {'county': 'Kent', 'town': 'Herne Bay'},
    {'county': 'Hertfordshire', 'town': 'Hertford'},
    {'county': 'North Humberside', 'town': 'Hessle'},
    {'county': 'Northumberland', 'town': 'Hexham'},
    {'county': 'Lancashire', 'town': 'Heywood'},
    {'county': 'Buckinghamshire', 'town': 'High Wycombe'},
    {'county': 'Somerset', 'town': 'Highbridge'},
    {'county': 'Co Down', 'town': 'Hillsborough'},
    {'county': 'Leicestershire', 'town': 'Hinckley'},
    {'county': 'Surrey', 'town': 'Hindhead'},
    {'county': 'Hertfordshire', 'town': 'Hitchin'},
    {'county': 'Essex', 'town': 'Hockley'},
    {'county': 'Hertfordshire', 'town': 'Hoddesdon'},
    {'county': 'Lincolnshire', 'town': 'Holbeach'},
    {'county': 'Cheshire', 'town': 'Holmes Chapel'},
    {'county': 'Devon', 'town': 'Holsworthy'},
    {'county': 'Norfolk', 'town': 'Holt'},
    {'county': 'Gwynedd', 'town': 'Holyhead'},
    {'county': 'Co Down', 'town': 'Holywood'},
    {'county': 'Lincolnshire', 'town': 'Honington'},
    {'county': 'Devon', 'town': 'Honiton'},
    {'county': 'Hampshire', 'town': 'Hook'},
    {'county': 'Surrey', 'town': 'Horley'},
    {'county': 'Lancashire', 'town': 'Hornby'},
    {'county': 'Essex', 'town': 'Hornchurch'},
    {'county': 'East Riding of Yorkshire', 'town': 'Hornsea'},
    {'county': 'West Sussex', 'town': 'Horsham'},
    {'county': 'Tyne & Wear', 'town': 'Houghton le Spring'},
    {'county': 'Middlesex', 'town': 'Hounslow'},
    {'county': 'East Sussex', 'town': 'Hove'},
    {'county': 'West Yorkshire', 'town': 'Huddersfield'},
    {'county': 'North Humberside', 'town': 'Hull'},
    {'county': 'Berkshire', 'town': 'Hungerford'},
    {'county': 'Norfolk', 'town': 'Hunstanton'},
    {'county': 'Cambridgeshire', 'town': 'Huntingdon'},
    {'county': 'Aberdeenshire', 'town': 'Huntly'},
    {'county': 'Cheshire', 'town': 'Hyde'},
    {'county': 'Kent', 'town': 'Hythe'},
    {'county': 'Essex', 'town': 'Ilford'},
    {'county': 'Devon', 'town': 'Ilfracombe'},
    {'county': 'Derbyshire', 'town': 'Ilkeston'},
    {'county': 'West Yorkshire', 'town': 'Ilkley'},
    {'county': 'South Humberside', 'town': 'Immingham'},
    {'county': 'Essex', 'town': 'Ingatestone'},
    {'county': 'Aberdeenshire', 'town': 'Insch'},
    {'county': 'Argyll', 'town': 'Inveraray'},
    {'county': 'Inverness-shire', 'town': 'Inverness'},
    {'county': 'Aberdeenshire', 'town': 'Inverurie'},
    {'county': 'Isle of Iona', 'town': 'Iona'},
    {'county': 'Staffordshire', 'town': 'Ipstones'},
    {'county': 'Suffolk', 'town': 'Ipswich'},
    {'county': 'Shropshire', 'town': 'Ironbridge'},
    {'county': 'Isle of Wight', 'town': 'Isle of Wight'},
    {'county': 'Middlesex', 'town': 'Isleworth'},
    {'county': 'Channel Islands', 'town': 'Jersey'},
    {'county': 'Renfrewshire', 'town': 'Johnstone'},
    {'county': 'West Yorkshire', 'town': 'Keighley'},
    {'county': 'Roxburghshire', 'town': 'Kelso'},
    {'county': 'Cumbria', 'town': 'Kendal'},
    {'county': 'Warwickshire', 'town': 'Kenilworth'},
    {'county': 'Cumbria', 'town': 'Keswick'},
    {'county': 'Northamptonshire', 'town': 'Kettering'},
    {'county': 'Hereford & Worcester', 'town': 'Kidderminster'},
    {'county': 'Ayrshire', 'town': 'Kilbirnie'},
    {'county': 'Perthshire', 'town': 'Killin'},
    {'county': 'Lincolnshire', 'town': 'Killingholme'},
    {'county': 'Renfrewshire', 'town': 'Kilmacolm'},
    {'county': 'Ayrshire', 'town': 'Kilmarnock'},
    {'county': 'Norfolk', 'town': 'King\'s Lynn'},
    {'county': 'Hertfordshire', 'town': 'Kings Langley'},
    {'county': 'Devon', 'town': 'Kingsbridge'},
    {'county': 'Surrey', 'town': 'Kingston upon Thames'},
    {'county': 'West Midlands', 'town': 'Kingswinford'},
    {'county': 'Herefordshire', 'town': 'Kington'},
    {'county': 'Inverness-shire', 'town': 'Kingussie'},
    {'county': 'Cumbria', 'town': 'Kirkby Stephen'},
    {'county': 'Fife', 'town': 'Kirkcaldy'},
    {'county': 'Northumberland', 'town': 'Kirkwhelpington'},
    {'county': 'Angus', 'town': 'Kirriemuir'},
    {'county': 'Powys', 'town': 'Knighton'},
    {'county': 'Cheshire', 'town': 'Knutsford'},
    {'county': 'Ross-shire', 'town': 'Kyle'},
    {'county': 'Isle of Skye', 'town': 'Kyleakin'},
    {'county': 'Essex', 'town': 'Laindon'},
    {'county': 'Sutherland', 'town': 'Lairg'},
    {'county': 'Ceredigion', 'town': 'Lampeter'},
    {'county': 'Lanarkshire', 'town': 'Lanark'},
    {'county': 'Lancashire', 'town': 'Lancaster'},
    {'county': 'West Sussex', 'town': 'Lancing'},
    {'county': 'Warwickshire', 'town': 'Lapworth'},
    {'county': 'Stirlingshire', 'town': 'Larbert'},
    {'county': 'Caithness', 'town': 'Latheron'},
    {'county': 'Cornwall', 'town': 'Launceston'},
    {'county': 'Warwickshire', 'town': 'Leamington Spa'},
    {'county': 'Surrey', 'town': 'Leatherhead'},
    {'county': 'Hereford & Worcester', 'town': 'Ledbury'},
    {'county': 'West Yorkshire', 'town': 'Leeds'},
    {'county': 'Leicestershire', 'town': 'Leicester'},
    {'county': 'Lancashire', 'town': 'Leigh'},
    {'county': 'Essex', 'town': 'Leigh-on-Sea'},
    {'county': 'Bedfordshire', 'town': 'Leighton Buzzard'},
    {'county': 'Suffolk', 'town': 'Leiston'},
    {'county': 'Hereford & Worcester', 'town': 'Leominster'},
    {'county': 'Isle of Shetland', 'town': 'Lerwick'},
    {'county': 'Hertfordshire', 'town': 'Letchworth'},
    {'county': 'East Sussex', 'town': 'Lewes'},
    {'county': 'North Yorkshire', 'town': 'Leyburn'},
    {'county': 'Lancashire', 'town': 'Leyland'},
    {'county': 'Staffordshire', 'town': 'Lichfield'},
    {'county': 'Surrey', 'town': 'Lightwater'},
    {'county': 'Co Londonderry', 'town': 'Limavady'},
    {'county': 'Lincolnshire', 'town': 'Lincoln'},
    {'county': 'Surrey', 'town': 'Lingfield'},
    {'county': 'Hampshire', 'town': 'Liphook'},
    {'county': 'Co Antrim', 'town': 'Lisburn'},
    {'county': 'Cornwall', 'town': 'Liskeard'},
    {'county': 'Hampshire', 'town': 'Liss'},
    {'county': 'Lancashire', 'town': 'Littleborough'},
    {'county': 'West Sussex', 'town': 'Littlehampton'},
    {'county': 'Merseyside', 'town': 'Liverpool'},
    {'county': 'West Lothian', 'town': 'Livingston'},
    {'county': 'Ceredigion', 'town': 'Llanarth'},
    {'county': 'Gwynedd', 'town': 'Llanbedr'},
    {'county': 'Carmarthenshire', 'town': 'Llandeilo'},
    {'county': 'Carmarthenshire', 'town': 'Llandovery'},
    {'county': 'Powys', 'town': 'Llandrindod Wells'},
    {'county': 'Gwynedd', 'town': 'Llandudno'},
    {'county': 'Dyfed', 'town': 'Llandysul'},
    {'county': 'Dyfed', 'town': 'Llanelli'},
    {'county': 'Clwyd', 'town': 'Llangollen'},
    {'county': 'Powys', 'town': 'Llanidloes'},
    {'county': 'Ceredigion', 'town': 'Llanon'},
    {'county': 'Gwynedd', 'town': 'Llanrwst'},
    {'county': 'South Glamorgan', 'town': 'Llantwit'},
    {'county': 'Dyfed', 'town': 'Llanwrda'},
    {'county': 'Powys', 'town': 'Llanwrtyd Wells'},
    {'county': 'Midlothian', 'town': 'Loanhead'},
    {'county': 'Isle of Uist', 'town': 'Lochboisdale'},
    {'county': 'Ross-shire', 'town': 'Lochcarron'},
    {'county': 'Argyll', 'town': 'Lochgilphead'},
    {'county': 'Renfrewshire', 'town': 'Lochwinnoch'},
    {'county': 'Dumfriesshire', 'town': 'Lockerbie'},
    {'county': 'London', 'town': 'London'},
    {'county': 'Co Londonderry', 'town': 'Londonderry'},
    {'county': 'Leicestershire', 'town': 'Loughborough'},
    {'county': 'Essex', 'town': 'Loughton'},
    {'county': 'Lincolnshire', 'town': 'Louth'},
    {'county': 'Suffolk', 'town': 'Lowestoft'},
    {'county': 'Shropshire', 'town': 'Ludlow'},
    {'county': 'Co Antrim', 'town': 'Lurgan'},
    {'county': 'Bedfordshire', 'town': 'Luton'},
    {'county': 'Leicestershire', 'town': 'Lutterworth'},
    {'county': 'Gloucestershire', 'town': 'Lydney'},
    {'county': 'Hampshire', 'town': 'Lymington'},
    {'county': 'Hampshire', 'town': 'Lyndhurst'},
    {'county': 'Devon', 'town': 'Lynton'},
    {'county': 'Lancashire', 'town': 'Lytham StAnnes'},
    {'county': 'Cheshire', 'town': 'Macclesfield'},
    {'county': 'Powys', 'town': 'Machynlleth'},
    {'county': 'Cambridgeshire', 'town': 'Madingley'},
    {'county': 'Mid Glamorgan', 'town': 'Maesteg'},
    {'county': 'Co Londonderry', 'town': 'Magharafelt'},
    {'county': 'Berkshire', 'town': 'Maidenhead'},
    {'county': 'Kent', 'town': 'Maidstone'},
    {'county': 'Essex', 'town': 'Maldon'},
    {'county': 'Wiltshire', 'town': 'Malmesbury'},
    {'county': 'Cheshire', 'town': 'Malpas'},
    {'county': 'North Yorkshire', 'town': 'Malton'},
    {'county': 'Hereford & Worcester', 'town': 'Malvern'},
    {'county': 'Greater Manchester', 'town': 'Manchester'},
    {'county': 'Nottinghamshire', 'town': 'Mansfield'},
    {'county': 'Cambridgeshire', 'town': 'March'},
    {'county': 'Kent', 'town': 'Margate'},
    {'county': 'Shropshire', 'town': 'Market Drayton'},
    {'county': 'Leicestershire', 'town': 'Market Harborough'},
    {'county': 'Lincolnshire', 'town': 'Market Rasen'},
    {'county': 'East Riding of Yorkshire', 'town': 'Market Weighton'},
    {'county': 'Wiltshire', 'town': 'Marlborough'},
    {'county': 'Buckinghamshire', 'town': 'Marlow'},
    {'county': 'Lincolnshire', 'town': 'Martin'},
    {'county': 'Cumbria', 'town': 'Maryport'},
    {'county': 'Derbyshire', 'town': 'Matlock'},
    {'county': 'Aberdeenshire', 'town': 'Maud'},
    {'county': 'Kent', 'town': 'Medway'},
    {'county': 'Powys', 'town': 'Meifod'},
    {'county': 'Wiltshire', 'town': 'Melksham'},
    {'county': 'Leicestershire', 'town': 'Melton Mowbray'},
    {'county': 'Wiltshire', 'town': 'Mere'},
    {'county': 'West Midlands', 'town': 'Meriden'},
    {'county': 'Mid Glamorgan', 'town': 'Merthyr Tydfil'},
    {'county': 'South Yorkshire', 'town': 'Mexborough'},
    {'county': 'Cleveland', 'town': 'Middlesbrough'},
    {'county': 'Cheshire', 'town': 'Middlewich'},
    {'county': 'West Sussex', 'town': 'Midhurst'},
    {'county': 'Suffolk', 'town': 'Mildenhall'},
    {'county': 'Pembrokeshire', 'town': 'Milford Haven'},
    {'county': 'Buckinghamshire', 'town': 'Milton Keynes'},
    {'county': 'Somerset', 'town': 'Minehead'},
    {'county': 'West Yorkshire', 'town': 'Mirfield'},
    {'county': 'Surrey', 'town': 'Mitcham'},
    {'county': 'Gloucestershire', 'town': 'Mitcheldean'},
    {'county': 'Clwyd', 'town': 'Mold'},
    {'county': 'Gwent', 'town': 'Monmouth'},
    {'county': 'Powys', 'town': 'Montgomery'},
    {'county': 'Angus', 'town': 'Montrose'},
    {'county': 'Surrey', 'town': 'Morden'},
    {'county': 'Lancashire', 'town': 'Morecambe'},
    {'county': 'Devon', 'town': 'Moretonhampstead'},
    {'county': 'Northumberiand', 'town': 'Morpeth'},
    {'county': 'East Ayrshire', 'town': 'Moscow'},
    {'county': 'Lanarkshire', 'town': 'Motherwell'},
    {'county': 'Midlothian', 'town': 'Musselburgh'},
    {'county': 'Avon', 'town': 'Nailsea'},
    {'county': 'Inverness-shire', 'town': 'Nairn'},
    {'county': 'Cheshire', 'town': 'Nantwich'},
    {'county': 'Pembrokeshire', 'town': 'Narberth'},
    {'county': 'Neath Port Talbot', 'town': 'Neath'},
    {'county': 'Gwynedd', 'town': 'Nefyn'},
    {'county': 'Lancashire', 'town': 'Nelson'},
    {'county': 'Inverness-shire', 'town': 'Nethy Bridge'},
    {'county': 'Surrey', 'town': 'New Malden'},
    {'county': 'Derbyshire', 'town': 'New Mills'},
    {'county': 'Nottinghamshire', 'town': 'Newark'},
    {'county': 'Berkshire', 'town': 'Newbury'},
    {'county': 'Co Down', 'town': 'Newcastle'},
    {'county': 'Staffordshire', 'town': 'Newcastle'},
    {'county': 'Dyfed', 'town': 'Newcastle Emlyn'},
    {'county': 'Tyne & Wear', 'town': 'Newcastle upon Tyne'},
    {'county': 'Roxburghshire', 'town': 'Newcastleton'},
    {'county': 'Gloucestershire', 'town': 'Newent'},
    {'county': 'East Sussex', 'town': 'Newhaven'},
    {'county': 'Suffolk', 'town': 'Newmarket'},
    {'county': 'Gwent', 'town': 'Newport'},
    {'county': 'Isle of Wight', 'town': 'Newport'},
    {'county': 'Shropshire', 'town': 'Newport'},
    {'county': 'Buckinghamshire', 'town': 'Newport Pagnell'},
    {'county': 'Cornwall', 'town': 'Newquay'},
    {'county': 'Devon', 'town': 'Newton Abbot'},
    {'county': 'Powys', 'town': 'Newtown'},
    {'county': 'Merseyside', 'town': 'Newtown-le- Willows'},
    {'county': 'Co Antrim', 'town': 'Newtownabbey'},
    {'county': 'Co Down', 'town': 'Newtownards'},
    {'county': 'East Lothian', 'town': 'North Berwick'},
    {'county': 'Tyne & Wear', 'town': 'North Shields'},
    {'county': 'Norfolk', 'town': 'North Walsham'},
    {'county': 'North Yorkshire', 'town': 'Northallerton'},
    {'county': 'Northamptonshire', 'town': 'Northampton'},
    {'county': 'Cheshire', 'town': 'Northwich'},
    {'county': 'Middlesex', 'town': 'Northwood'},
    {'county': 'Norfolk', 'town': 'Norwich'},
    {'county': 'Nottinghamshire', 'town': 'Nottingham'},
    {'county': 'Nottinghamshire', 'town': 'Nottinghamshire'},
    {'county': 'Warwickshire', 'town': 'Nuneaton'},
    {'county': 'Leicestershire', 'town': 'Oakham'},
    {'county': 'Argyll', 'town': 'Oban'},
    {'county': 'Devon', 'town': 'Okehampton'},
    {'county': 'Lancashire', 'town': 'Oldham'},
    {'county': 'Co Tyrone', 'town': 'Omagh'},
    {'county': 'Essex', 'town': 'Ongar'},
    {'county': 'Lancashire', 'town': 'Ormskirk'},
    {'county': 'Kent', 'town': 'Orpington'},
    {'county': 'West Yorkshire', 'town': 'Ossett'},
    {'county': 'Shropshire', 'town': 'Oswestry'},
    {'county': 'West Yorkshire', 'town': 'Otley'},
    {'county': 'Oxfordshire', 'town': 'Oxford'},
    {'county': 'Surrey', 'town': 'Oxted'},
    {'county': 'Devon', 'town': 'Paignton'},
    {'county': 'Renfrewshire', 'town': 'Paisley'},
    {'county': 'Suffolk', 'town': 'Pakenham'},
    {'county': 'Cornwall', 'town': 'Par'},
    {'county': 'Dyfed', 'town': 'Pembroke'},
    {'county': 'South Glamorgan', 'town': 'Penarth'},
    {'county': 'Herefordshire', 'town': 'Pencombe'},
    {'county': 'Midlothian', 'town': 'Penicuik'},
    {'county': 'Gwynedd', 'town': 'Penmaenmawr'},
    {'county': 'Gwynedd', 'town': 'Penrhyndeudraeth'},
    {'county': 'Cumbria', 'town': 'Penrith'},
    {'county': 'Cornwall', 'town': 'Penryn'},
    {'county': 'Cornwall', 'town': 'Penzance'},
    {'county': 'Hereford & Worcester', 'town': 'Pershore'},
    {'county': 'Perthshire', 'town': 'Perth'},
    {'county': 'Cambridgeshire', 'town': 'Peterborough'},
    {'county': 'Aberdeenshire', 'town': 'Peterhead'},
    {'county': 'Hampshire', 'town': 'Petersfield'},
    {'county': 'West Sussex', 'town': 'Petworth'},
    {'county': 'East Sussex', 'town': 'Pevensey'},
    {'county': 'Wiltshire', 'town': 'Pewsey'},
    {'county': 'North Yorkshire', 'town': 'Pickering'},
    {'county': 'Middlesex', 'town': 'Pinner'},
    {'county': 'Perthshire', 'town': 'Pitlochry'},
    {'county': 'Devon', 'town': 'Plymouth'},
    {'county': 'East Riding of Yorkshire', 'town': 'Pocklington'},
    {'county': 'West Yorkshire', 'town': 'Pontefract'},
    {'county': 'Mid Glamorgan', 'town': 'Pontyclun'},
    {'county': 'Torfaen', 'town': 'Pontypool'},
    {'county': 'Mid Glamorgan', 'town': 'Pontypridd'},
    {'county': 'Dorset', 'town': 'Poole'},
    {'county': 'Cumbria', 'town': 'Pooley Bridge'},
    {'county': 'Cornwall', 'town': 'Port Isaac'},
    {'county': 'West Glamorgan', 'town': 'Port Talbot'},
    {'county': 'Mid Glamorgan', 'town': 'Porthcawl'},
    {'county': 'Gwynedd', 'town': 'Porthmadog'},
    {'county': 'Isle of Skye', 'town': 'Portree'},
    {'county': 'Co Antrim', 'town': 'Portrush'},
    {'county': 'Hampshire', 'town': 'Portsmouth'},
    {'county': 'Hertfordshire', 'town': 'Potters Bar'},
    {'county': 'Lancashire', 'town': 'Poulton-le-Fylde'},
    {'county': 'Merseyside', 'town': 'Prescot'},
    {'county': 'Clwyd', 'town': 'Prestatyn'},
    {'county': 'Lancashire', 'town': 'Preston'},
    {'county': 'Ayrshire', 'town': 'Prestwick'},
    {'county': 'Buckinghamshire', 'town': 'Princes Risborough'},
    {'county': 'Northumberland', 'town': 'Prudhoe'},
    {'county': 'West Sussex', 'town': 'Pulborough'},
    {'county': 'Surrey', 'town': 'Purley'},
    {'county': 'Gwynedd', 'town': 'Pwllheli'},
    {'county': 'Hertfordshire', 'town': 'Radlett'},
    {'county': 'Isle of Man', 'town': 'Ramsey'},
    {'county': 'Kent', 'town': 'Ramsgate'},
    {'county': 'Cumbria', 'town': 'Raughton Head'},
    {'county': 'Essex', 'town': 'Rayleigh'},
    {'county': 'Berkshire', 'town': 'Reading'},
    {'county': 'Cleveland', 'town': 'Redcar'},
    {'county': 'Hereford and', 'town': 'Redditch'},
    {'county': 'Surrey', 'town': 'Redhill'},
    {'county': 'Cornwall', 'town': 'Redruth'},
    {'county': 'Surrey', 'town': 'Reigate'},
    {'county': 'Nottmghamshire', 'town': 'Retford'},
    {'county': 'Clwyd', 'town': 'Rhyl'},
    {'county': 'North Yorkshire', 'town': 'Richmond'},
    {'county': 'Surrey', 'town': 'Richmond'},
    {'county': 'Hertfordshire', 'town': 'Rickmansworth'},
    {'county': 'Northumberland', 'town': 'Riding Mill'},
    {'county': 'Hampshire', 'town': 'Ringwood'},
    {'county': 'Derbyshire', 'town': 'Ripley'},
    {'county': 'North Yorkshire', 'town': 'Ripon'},
    {'county': 'East Sussex', 'town': 'Robertsbridge'},
    {'county': 'Lancashire', 'town': 'Rochdale'},
    {'county': 'Kent', 'town': 'Rochester'},
    {'county': 'Essex', 'town': 'Rochford'},
    {'county': 'Hampshire', 'town': 'Rockbourne'},
    {'county': 'Essex', 'town': 'Romford'},
    {'county': 'Hampshire', 'town': 'Romsey'},
    {'county': 'Herefordshire', 'town': 'Ross-on-Wye'},
    {'county': 'Lancashire', 'town': 'Rossendale'},
    {'county': 'Northumberland', 'town': 'Rothbury'},
    {'county': 'South Yorkshire', 'town': 'Rotherham'},
    {'county': 'Isle ofBute', 'town': 'Rothesay'},
    {'county': 'Hertfordshire', 'town': 'Royston'},
    {'county': 'Warwickshire', 'town': 'Rugby'},
    {'county': 'Staffordshire', 'town': 'Rugeley'},
    {'county': 'Middlesex', 'town': 'Ruislip'},
    {'county': 'Cheshire', 'town': 'Runcorn'},
    {'county': 'Northamptonshire', 'town': 'Rushden'},
    {'county': 'Clwyd', 'town': 'Ruthin'},
    {'county': 'East Sussex', 'town': 'Rye'},
    {'county': 'Tyne & Wear', 'town': 'Ryton'},
    {'county': 'Essex', 'town': 'Saffron Walden'},
    {'county': 'Lancashire', 'town': 'Salford'},
    {'county': 'Wiltshire', 'town': 'Salisbury'},
    {'county': 'Cornwall', 'town': 'Saltash'},
    {'county': 'Cleveland', 'town': 'Saltburn-by-the-Sea'},
    {'county': 'Ayrshire', 'town': 'Saltcoats'},
    {'county': 'Cheshire', 'town': 'Sandbach'},
    {'county': 'Berkshire', 'town': 'Sandhurst'},
    {'county': 'Isle of Wight', 'town': 'Sandown'},
    {'county': 'Kent', 'town': 'Sandwich'},
    {'county': 'Bedfordshire', 'town': 'Sandy'},
    {'county': 'Dumfriesshire', 'town': 'Sanquhar'},
    {'county': 'Hertfordshire', 'town': 'Sawbridgeworth'},
    {'county': 'Suffolk', 'town': 'Saxmundham'},
    {'county': 'North Yorkshire', 'town': 'Scarborough'},
    {'county': 'Isle of Tiree', 'town': 'Scarinish'},
    {'county': 'South Humberside', 'town': 'Scunthorpe'},
    {'county': 'East Sussex', 'town': 'Seaford'},
    {'county': 'Co Durham', 'town': 'Seaham'},
    {'county': 'Northumberland', 'town': 'Seahouses'},
    {'county': 'Devon', 'town': 'Seaton'},
    {'county': 'Cumbria', 'town': 'Sedbergh'},
    {'county': 'Co Durham', 'town': 'Sedgefield'},
    {'county': 'North Yorkshire', 'town': 'Selby'},
    {'county': 'Selkirkshire', 'town': 'Selkirk'},
    {'county': 'North Yorkshire', 'town': 'Settle'},
    {'county': 'Kent', 'town': 'Sevenoaks'},
    {'county': 'Wiltshire', 'town': 'Shaftesbury'},
    {'county': 'Cumbria', 'town': 'Shap'},
    {'county': 'Isle of Lewis', 'town': 'Shawbost'},
    {'county': 'South Yorkshire', 'town': 'Sheffield'},
    {'county': 'Middlesex', 'town': 'Shepperton'},
    {'county': 'Somerset', 'town': 'Shepton Mallet'},
    {'county': 'Dorset', 'town': 'Sherborne'},
    {'county': 'Norfolk', 'town': 'Sheringham'},
    {'county': 'Isle of Shetland', 'town': 'Shetland'},
    {'county': 'Shropshire', 'town': 'Shifnal'},
    {'county': 'West Yorkshire', 'town': 'Shipley'},
    {'county': 'Shropshire', 'town': 'Shrewsbury'},
    {'county': 'Kent', 'town': 'Sidcup'},
    {'county': 'Devon', 'town': 'Sidmouth'},
    {'county': 'Kent', 'town': 'Sittingbourne'},
    {'county': 'Lincolnshire', 'town': 'Skegness'},
    {'county': 'Lancashire', 'town': 'Skelmersdale'},
    {'county': 'North Yorkshire', 'town': 'Skipton'},
    {'county': 'Lincolnshire', 'town': 'Sleaford'},
    {'county': 'Berkshire', 'town': 'Slough'},
    {'county': 'West Midlands', 'town': 'Solihull'},
    {'county': 'Surrey', 'town': 'South Croydon'},
    {'county': 'West Lothian', 'town': 'South Queensferry'},
    {'county': 'Devon', 'town': 'South Molton'},
    {'county': 'Somerset', 'town': 'South Petherton'},
    {'county': 'Merseyside', 'town': 'South Wirral'},
    {'county': 'Middlesex', 'town': 'Southall'},
    {'county': 'Warwickshire', 'town': 'Southam'},
    {'county': 'Hampshire', 'town': 'Southampton'},
    {'county': 'Essex', 'town': 'Southend-on-Sea'},
    {'county': 'Essex', 'town': 'Southminster'},
    {'county': 'Merseyside', 'town': 'Southport'},
    {'county': 'Hampshire', 'town': 'Southsea'},
    {'county': 'Nottinghamshire', 'town': 'Southwell'},
    {'county': 'North Yorkshire', 'town': 'Sowerby'},
    {'county': 'Lincolnshire', 'town': 'Spalding'},
    {'county': 'Lincolnshire', 'town': 'Spilsby'},
    {'county': 'Hertfordshire', 'town': 'St Albans'},
    {'county': 'Fife', 'town': 'St Andrews'},
    {'county': 'Clwyd', 'town': 'St Asaph'},
    {'county': 'Cornwall', 'town': 'St Austell'},
    {'county': 'Carmarthenshire', 'town': 'St Clears'},
    {'county': 'Merseyside', 'town': 'St Helens'},
    {'county': 'Cornwall', 'town': 'St Ives'},
    {'county': 'East Sussex', 'town': 'St Leonards-on-Sea'},
    {'county': 'Staffordshire', 'town': 'Stafford'},
    {'county': 'Middlesex', 'town': 'Staines'},
    {'county': 'Lincolnshire', 'town': 'Stamford'},
    {'county': 'Essex', 'town': 'Stanford-le-Hope'},
    {'county': 'Middlesex', 'town': 'Stanmore'},
    {'county': 'Hertfordshire', 'town': 'Stevenage'},
    {'county': 'Stirlingshire', 'town': 'Stirling'},
    {'county': 'Cheshire', 'town': 'Stockport'},
    {'county': 'Northumberland', 'town': 'Stocksfield'},
    {'county': 'Cleveland', 'town': 'Stockton-on-Tees'},
    {'county': 'Staffordshire', 'town': 'Stoke-on-Trent'},
    {'county': 'Staffordshire', 'town': 'Stone'},
    {'county': 'Kincardineshire', 'town': 'Stonehaven'},
    {'county': 'Isle of Lewis', 'town': 'Stornoway'},
    {'county': 'West Midlands', 'town': 'Stourbridge'},
    {'county': 'Hereford & Worcester', 'town': 'Stourport-on-Severn'},
    {'county': 'Gloucestershire', 'town': 'Stow-on-the-Wold'},
    {'county': 'Suffolk', 'town': 'Stowmarket'},
    {'county': 'Wigtownshire', 'town': 'Stranraer'},
    {'county': 'Warwickshire', 'town': 'Stratford-upon-Avon'},
    {'county': 'Ross-shire', 'town': 'Strathcarron'},
    {'county': 'South Lanarkshire', 'town': 'Strathaven'},
    {'county': 'Ross-shire', 'town': 'Strathpeffer'},
    {'county': 'Somerset', 'town': 'Street'},
    {'county': 'Gloucestershire', 'town': 'Stroud'},
    {'county': 'Suffolk', 'town': 'Sudbury'},
    {'county': 'Middlesex', 'town': 'Sunbury-on-Thames'},
    {'county': 'Tyne & Wear', 'town': 'Sunderland'},
    {'county': 'Surrey', 'town': 'Surbiton'},
    {'county': 'Surrey', 'town': 'Sutton'},
    {'county': 'West Midlands', 'town': 'Sutton Coldfield'},
    {'county': 'Nottinghamshire', 'town': 'Sutton-in-Ashfield'},
    {'county': 'Norfolk', 'town': 'Swaffham'},
    {'county': 'Dorset', 'town': 'Swanage'},
    {'county': 'Kent', 'town': 'Swanley'},
    {'county': 'West Glamorgan', 'town': 'Swansea'},
    {'county': 'Wiltshire', 'town': 'Swindon'},
    {'county': 'Ross-shire', 'town': 'Tain'},
    {'county': 'Gwynedd', 'town': 'Talybont'},
    {'county': 'Staffordshire', 'town': 'Tamworth'},
    {'county': 'Argyll', 'town': 'Tarbert'},
    {'county': 'Cheshire', 'town': 'Tarporley'},
    {'county': 'Somerset', 'town': 'Taunton'},
    {'county': 'Devon', 'town': 'Tavistock'},
    {'county': 'Middlesex', 'town': 'Teddington'},
    {'county': 'Devon', 'town': 'Teignmouth'},
    {'county': 'Shropshire', 'town': 'Telford'},
    {'county': 'Somerset', 'town': 'Temple Cloud'},
    {'county': 'Somerset', 'town': 'Templecombe'},
    {'county': 'Dyfed', 'town': 'Tenby'},
    {'county': 'Gloucestershire', 'town': 'Tewkesbury'},
    {'county': 'Oxfordshire', 'town': 'Thame'},
    {'county': 'Kent', 'town': 'Thanet'},
    {'county': 'Berkshire', 'town': 'Thatcham'},
    {'county': 'Norfolk', 'town': 'Thetford'},
    {'county': 'North Yorkshire', 'town': 'Thirsk'},
    {'county': 'Surrey', 'town': 'Thornton Heath'},
    {'county': 'Caithness', 'town': 'Thurso'},
    {'county': 'Essex', 'town': 'Tilbury'},
    {'county': 'West Midlands', 'town': 'Tipton'},
    {'county': 'Devon', 'town': 'Tiverton'},
    {'county': 'West Yorkshire', 'town': 'Todmorden'},
    {'county': 'Kent', 'town': 'Tonbridge'},
    {'county': 'Devon', 'town': 'Torquay'},
    {'county': 'Devon', 'town': 'Torrington'},
    {'county': 'Isle of Wight', 'town': 'Totland Bay'},
    {'county': 'Northamptonshire', 'town': 'Towcester'},
    {'county': 'East Lothian', 'town': 'Tranent'},
    {'county': 'Gwent', 'town': 'Tredegar'},
    {'county': 'Hertfordshire', 'town': 'Tring'},
    {'county': 'Wiltshire', 'town': 'Trowbridge'},
    {'county': 'Cornwall', 'town': 'Truro'},
    {'county': 'Kent', 'town': 'Tunbridge Wells'},
    {'county': 'Aberdeenshire', 'town': 'Turriff'},
    {'county': 'Middlesex', 'town': 'Twickenham'},
    {'county': 'Gwynedd', 'town': 'Tywyn'},
    {'county': 'East Sussex', 'town': 'Uckfield'},
    {'county': 'Cumbria', 'town': 'Ulverston'},
    {'county': 'Devon', 'town': 'Umberleigh'},
    {'county': 'Staffordshire', 'town': 'Uttoxeter'},
    {'county': 'Middlesex', 'town': 'Uxbridge'},
    {'county': 'Isle ofWight', 'town': 'Ventnor'},
    {'county': 'Cornwall', 'town': 'Wadebridge'},
    {'county': 'West Yorkshire', 'town': 'Wakefield'},
    {'county': 'Merseyside', 'town': 'Wallasey'},
    {'county': 'Oxfordshire', 'town': 'Wallingford'},
    {'county': 'Surrey', 'town': 'Wallington'},
    {'county': 'West Midlands', 'town': 'Walsall'},
    {'county': 'Norfolk', 'town': 'Walsingham'},
    {'county': 'Hertfordshire', 'town': 'Waltham Cross'},
    {'county': 'Essex', 'town': 'Walton on the Naze'},
    {'county': 'Surrey', 'town': 'Walton-on-Thames'},
    {'county': 'Oxfordshire', 'town': 'Wantage'},
    {'county': 'Cambridgeshire', 'town': 'Warboys'},
    {'county': 'Hertfordshire', 'town': 'Ware'},
    {'county': 'Dorset', 'town': 'Wareham'},
    {'county': 'West Midlands', 'town': 'Warley'},
    {'county': 'Wiltshire', 'town': 'Warminster'},
    {'county': 'Cheshire', 'town': 'Warrington'},
    {'county': 'Warwickshire', 'town': 'Warwick'},
    {'county': 'Warwickshire', 'town': 'Warwickshire'},
    {'county': 'Tyne & Wear', 'town': 'Washington'},
    {'county': 'Somerset', 'town': 'Watchet'},
    {'county': 'Hertfordshire', 'town': 'Watford'},
    {'county': 'Somerset', 'town': 'Wedmore'},
    {'county': 'Kent', 'town': 'Welling'},
    {'county': 'Northamptonshire', 'town': 'Wellingborough'},
    {'county': 'Somerset', 'town': 'Wells'},
    {'county': 'Norfolk', 'town': 'Wells-next-the-Sea'},
    {'county': 'Powys', 'town': 'Welshpool'},
    {'county': 'Hertfordshire', 'town': 'Welwyn'},
    {'county': 'Hertfordshire', 'town': 'Welwyn Garden City'},
    {'county': 'Shropshire', 'town': 'Wem'},
    {'county': 'Middlesex', 'town': 'Wembley'},
    {'county': 'West Midlands', 'town': 'West Bromwich'},
    {'county': 'Surrey', 'town': 'West Byfleet'},
    {'county': 'Middlesex', 'town': 'West Drayton'},
    {'county': 'North Yorkshire', 'town': 'West Heslerton'},
    {'county': 'Ayrshire', 'town': 'West Kilbride'},
    {'county': 'Peeblesshire', 'town': 'West Linton'},
    {'county': 'Kent', 'town': 'West Malling'},
    {'county': 'Kent', 'town': 'West Wickham'},
    {'county': 'Wiltshire', 'town': 'Westbury'},
    {'county': 'Essex', 'town': 'Westcliff-on-Sea'},
    {'county': 'Kent', 'town': 'Westerham'},
    {'county': 'Avon', 'town': 'Weston-super-Mare'},
    {'county': 'West Yorkshire', 'town': 'Wetherby'},
    {'county': 'Surrey', 'town': 'Weybridge'},
    {'county': 'Dorset', 'town': 'Weymouth'},
    {'county': 'Nottinghamshire', 'town': 'Whatton'},
    {'county': 'North Yorkshire', 'town': 'Whitby'},
    {'county': 'Hampshire', 'town': 'Whitchurch'},
    {'county': 'Shropshire', 'town': 'Whitchurch'},
    {'county': 'Cumbria', 'town': 'Whitehaven'},
    {'county': 'Dyfed', 'town': 'Whitland'},
    {'county': 'Tyne & Wear', 'town': 'Whitley Bay'},
    {'county': 'Kent', 'town': 'Whitstable'},
    {'county': 'Caithness', 'town': 'Wick'},
    {'county': 'Essex', 'town': 'Wickford'},
    {'county': 'Lancashire', 'town': 'Wigan'},
    {'county': 'Cumbria', 'town': 'Wigton'},
    {'county': 'Cheshire', 'town': 'Wilmslow'},
    {'county': 'Dorset', 'town': 'Wimborne'},
    {'county': 'Somerset', 'town': 'Wincanton'},
    {'county': 'Hampshire', 'town': 'Winchester'},
    {'county': 'Cumbria', 'town': 'Windermere'},
    {'county': 'Berkshire', 'town': 'Windsor'},
    {'county': 'Somerset', 'town': 'Winscombe'},
    {'county': 'Merseyside', 'town': 'Wirral'},
    {'county': 'Cambridgeshire', 'town': 'Wisbech'},
    {'county': 'Lanarkshire', 'town': 'Wishaw'},
    {'county': 'Buckinghamshire', 'town': 'Witham'},
    {'county': 'Essex', 'town': 'Witham'},
    {'county': 'Oxfordshire', 'town': 'Witney'},
    {'county': 'Surrey', 'town': 'Woking'},
    {'county': 'Berkshire', 'town': 'Wokingham'},
    {'county': 'West Midlands', 'town': 'Wolverhampton'},
    {'county': 'Essex', 'town': 'Woodford Green'},
    {'county': 'Hereford & Worcester', 'town': 'Worcester'},
    {'county': 'Cumbria', 'town': 'Workington'},
    {'county': 'Nottinghamshire', 'town': 'Worksop'},
    {'county': 'Herefordshire', 'town': 'Wormbridge'},
    {'county': 'West Sussex', 'town': 'Worthing'},
    {'county': 'Gloucestershire', 'town': 'Wotton-under-Edge'},
    {'county': 'Clwyd', 'town': 'Wrexham'},
    {'county': 'Norfolk', 'town': 'Wymondham'},
    {'county': 'Surrey', 'town': 'Yateley'},
    {'county': 'Devon', 'town': 'Yelverton'},
    {'county': 'Somerset', 'town': 'Yeovil'},
    {'county': 'North Yorkshire', 'town': 'York'}
];

function flatMap (collection, mappingFn) {
    const flattened = [];

    for (const item of collection) {
        const value = mappingFn(item);

        if (typeof value[Symbol.iterator] === 'function') {
            flattened.push(...value);
            continue;
        }

        flattened.push(value);
    }
    return flattened;
}

function prop (key) {
  return function(obj) {
    if (obj == null) {
      return;
    }
    return obj[key];
  }
}
  
const groupedLocations = Map.groupBy(locations, ({town}) => town);

Tests:

Native JS flatMap
Array.from(groupedLocations) .flatMap(([k, v]) => v.length > 1 ? [[k, v.map(({county}) => county)]] : [])
Custom flatMap
flatMap( groupedLocations, ([k, v]) => v.length > 1 ? [[k, v.map(prop('county'))]]: [] )
lodash flatmap
_.flatMap( _.toArray(groupedLocations), ([k, v]) => v.length > 1 ? [[k, _.map(v, 'county')]]: [] )

Run results for: Custom Flatmap

Comparison between using JS' native flatMap, a custom flatMap, and lodash's flatMap. Custom flatMap works with all Iterable types, so need to convert Map's to arrays before flatMapping.

Native JS flatMap

Custom flatMap

lodash flatmap