London gaps

Inspired by this post, I've created a map showing exactly how well covered London is by rail services (click to enlarge). Tube stations are blue, DLR and Tramlink stops are green and National Rail stations are grey. The blobs indicate the area within a quarter mile and a half mile of each station, so anywhere the background is visible is outside the easy walking distance of one. The light grey area is Greater London and the white area is Travelcard Zone 3.

Update: A better version, with labels.

All data sourced from the Google Earth Community: Tube stations, National Rail stations, DLR stations, Tramlink stops and the Greater London boundary. Map created using a combination of grep hacks, PHP and Inkscape.