Administrative boundaries don't always reflect the way we live and work. Most are historical rather than practical, and you may well live in one but work in another.
It's for this reason that Travel To Work Areas were devised. TTWAs are self-contained areas in which most people both live and work. They approximate to labour markets, so are useful to government and other civil bodies for planning purposes. TTWAs are based on statistical analysis rather than administrative boundaries, and generated by computer algorithm. They're produced using census data, so evolve over time. The latest set of TTWAs was published in 2015. [data]
Criteria for defining TTWAs:
• at least 75% of the area's resident workforce work in the area
• at least 75% of the people who work in the area live in the area
• the area has an economically active population of at least 3500
To avoid splintering, the 75% limit can sometimes be lowered to 66.7%. But essentially, in every TTWA at least three-quarters of the workforce live there and at least three-quarters of the population work there.
It's not about individual people. If you live in one TTWA and work in another you don't disprove the statistics. It's just that everybody else outnumbers you.
There are currently 149 TTWAs in England, 45 in Scotland, 18 in Wales, 10 in Northern Ireland and 6 which cross a border. The number of TTWAs has decreased because people now tend to commute longer distances to work. In 1991 it took 308 TTWAs to cover the UK, in 2001 this fell to 243 and in 2011 there was a further reduction to 228.
Looking for example at the TTWAs in Essex, the largest is based around Chelmsford. This doesn't mean that most of the population work in Chelmsford, just that they work somewhere within the Chelmsford zone. Colchester is at the heart of a separate TTWA, while Clacton's isolated location carves out another TTWA beyond that. The south of the county forms a distinct TTWA based around Southend, while a goodly chunk of Epping Forest is beholden to London. As for northwest Essex, the influence of Cambridge spreads well across the county line. You can see how this viewpoint might be useful for planning purposes.
The TTWA with the...
» highest employment rate - Northallerton (84%)
» lowest employment rate - Hartlepool (64%)
» highest male employment rate - Taunton (90%)
» highest female employment rate - Worthing (82%)
» highest self-employment rate - Evesham (21%)
» lowest self-employment rate - Whitehaven (4%)
» most economically active population - Gloucester (87%)
» most economically inactive population - Clacton (31%)
The most populous TTWA, unsurprisingly, is London, with 8.4 million residents. It's followed by Manchester (2.7m) and Birmingham (1.7m), some distance behind. But in fourth place comes the TTWA of 'Slough and Heathrow' (1.7m), because London isn't necessarily the economic entity you think it is.
The Slough and Heathrow TTWA includes Maidenhead and Windsor, plus a chunk of north Surrey from Egham to Esher. But the influence of Heathrow also brings the whole of Hillingdon inside the TTWA, plus most of Hounslow and Richmond, much of Ealing and Kingston and a corner of Harrow. Perivale's in, Alperton's out. Brentford's in, Chiswick's out. Surbiton's in, New Malden's out. Remember this doesn't mean that most people in west London work at the airport, just that when the algorithm was drawing a dividing line this was the best place to put it.
Everyone else who lives in Greater London falls within the London TTWA. But the London TTWA also spreads well beyond the administrative boundary, confirming the importance of commuting into the capital from the fringes of the Home Counties. Let's explore the boundaries of 'London' more carefully.
In London TTWA
Not in London TTWA
Borehamwood, Potters Bar
Broxbourne, Dartford and Epsom & Ewell are the three out-of-London boroughs to fall entirely within the London TTWA. Hertsmere and Gravesham very nearly do. Epping Forest and Thurrock mostly do.
If government were ever minded to redraw the boundaries of Greater London, then taking the limits of the TTWA into account might be an appropriate idea - certainly better than taking the M25 as an arbitrary line. There are good reasons why administrative boundaries should perhaps better match economic activity, but also many other factors to take into account, indeed adopting boundaries based on a computer algorithm updated every ten years would be markedly irresponsible. Interesting, though.
Here's some further reading from the House of Commons library if you'd like to explore the issues further.