There are many concentric definitions of London. This probably isn’t an exhaustive list of the potential boundaries, but let’s give it a go. (For this version, there aren’t any links, nor are there maps. Consider this a work of geography, not cartography.)
or, Roman London. Defined by London Wall, the remains of which are still visible. Tiny, but still more or less discernable.
The City Of London
Historic, rich, and a strange sort of local authority, the City is (just over) a mile square (hence its nickname) on the north bank of the Thames (although it maintains four road bridges, and one footbridge). Find its boundaries by looking for griffins on poles.
The Cities of London and Westminster
Combine the old centres, which meet on the Thames, and you have this double-headed beast (and parliamentary consitituency, although excludes the northern part of the Borough of Westminster).
The Inner Ring Road
A selection of numbered roads provides the boundary for the central Congestion Charge area, and one definition of “central London”.
The Civil War Defences
Built in 1642 to defend the Parliamentary capital, 11 miles of wall take in an area from Shoreditch to Hyde Park, and Vauxhall to Rotherhithe.
Transport for London’s central fare boundary, which reaches a bit beyond the ring road. Of course, with nine zones, there are further boundaries outside this one, useful for bragging rights (and saving money on a Travelcard).
In 1990, Ofcom broke London’s old 01 telephone code in two, introducing 071. After two more changes, the city now has a single area code, 020, but there’s still plenty of numbers (and people who’ll remove the space) to testify to the old distinction the between “inner” and “outer” codes.
Originally defined in the Metropolis Management Act of 1855, finally given a sane system of government in 1889 (as London County Council) and lingering since 1965 as a definition for local government financing, these twelve modern London boroughs (and the City) form a large, but not all-encompassing, core.
Inside the Circulars
The North Circular, a hodge-podge of custom-built dual carriageway and converted streets, and the South Circular, which is barely a trunk road at all, form a ring around a certain definition of the place.
The London Postal District
Taking in eight postcode areas, this area’s been slowly contracting for years. Even bits of TfL’s zone 4 are outside it.
The larger, current, telephone code for London, which manages to not match the legislative boundary at all.
The Green Belt
Aimed at ending sprawl after the war, the green belt more or less worked. Its inner boundary stopped London’s expansion (especially in the north-west, where the Tube was once to have been extended.)
Defined in 1963, made a council in 1965, and currently the area that elects the London Mayor, eight MEPs, and 25 GLA members. This is the fuzzy shape most Londoners will recognise as a map of their city, I’d say.
Planned as part of the post-war London Ringway schemes, mangled to fit, and labelled the Road to Hell, the London Orbital - 120 miles long, and roughly 15 miles from the centre - is a usefully physical boundary to the city.
TfL Zone 9
You can get outside the M25 by Tube, even without going to zone 9 (Epping, on the Central Line), but by going into the strange new zones that used to be letters, you can get a long way north-west, into the wilds of Buckinghamshire.
Travel to Work Region
London’s economic impact sprawls well beyond any of these relatively well known (if messy) boundaries. A map drawn to define an area such that it contain 85% of those working within it reaches the Essex coast, nearly to Cambridge, and most of the way to Brighton. Similarly, one that allows up to 25% of people to be commuters draws in districts up to 30 miles away.
After that, London’s influence bleeds away, to be submerged in the rest of the south east.
(This is a response of sorts to Oliver O’Brien’s piece, Where is London?)