Explore every street in London

London is not a city you finish. It is a city you pick a piece of — and the way you pick that piece determines whether covering it is satisfying or endless.

Be honest with yourself first: you are not going to cover London. Greater London is enormous, its street network is one of the densest in Europe, and people who have walked it seriously for years talk in terms of boroughs rather than the whole.

That is not a reason not to start. It is a reason to scope it properly, because the difference between "covering London" and "covering my bit of London" is the difference between a project and a treadmill.

Pick a boundary and mean it

The single most useful thing you can do on day one is decide what counts.

Reasonable choices, roughly in order of difficulty:

The trap is leaving it open-ended. An unbounded London map never gets closer to anything, and the whole pleasure of this is watching a defined area fill in.

What London does that other cities do not

The alleys. The City and the older parts of the centre are threaded with courts, yards, passages and steps that have existed for centuries and appear on no driving route. This is the richest unclaimed ground in the country and almost all of it is walk-only.

The mews. Whole networks of them behind the Georgian terraces, most ending in nothing. They are dead ends, which means each one is an out-and-back, which means covering a mews-heavy district takes far longer than its area suggests.

The river. The Thames is a hard boundary with a limited number of crossings, and east of Tower Bridge they get sparse fast. North and south London are effectively two projects joined at a few points.

The parks and commons. Paths through Hampstead Heath, Richmond, Wimbledon Common and the rest are real ground that most map data handles poorly. On a square-based map they count exactly like streets, which makes a morning on the Heath unusually productive.

The realistic rhythm

The first month is easy: everything near you is new. The second is where people stall, because the frontier has moved out to the edge of comfortable walking distance and ordinary trips stop changing the picture.

What gets people through it is the shift from routes to gaps — opening the map, finding the holes, and going to fill them deliberately. In London those holes are almost always mews, estate interiors, footbridges and park paths, and getting them means walking somewhere specifically to walk it.

The Tube helps more than you would think. Out on one line, walk a district properly, back on another. It turns an unreachable part of the map into an afternoon.

Where to start today

If you have no better idea: pick the square kilometre around where you live and finish it. All of it — the cul-de-sacs, the estate paths, the bit behind the shops. It takes a few weeks of ordinary walking, and it teaches you what "covered" actually means before you commit to anything larger.

Get the iPhone beta — free, through TestFlight — or open the web app. The map starts blacked out, including the street you live on.