Greater London is thirty-two boroughs and the City, and no single description covers the driving in all of it. A collection in Belgravia and one in Chingford are the same booking with entirely different problems: one is about finding legal kerb space in a controlled zone, the other is about the North Circular at the wrong hour.
The ring roads do the organising. The A406 North Circular and the A205 South Circular close a loop around the inner boroughs, the M25 closes a much wider one outside them, and the radial roads — the A1, A4, A12, A13, A23, A3 and A40 — run between the two. Which of them a journey uses tells you more about its length than the mileage does.
The airports are the other constant. Heathrow serves the west, Gatwick the south, London City the east and centre, and Luton and Stansted the north and north-east. Every one of the London area pages under this index names the airports that place actually uses, with an indicative door-to-terminal drive and a road distance for each.