On Mon, 29 Oct 2007, Mr Thant wrote:

On 29 Oct, 11:04, "Clive D. W. Feather" cl...@on-the-
train.demon.co.uk wrote:

When you've finished, the grid holds the distance to the nearest
station. Convert it to a GIF and fiddle with the colour map and, for
example, you can have a map where places within 1km of a station are
green, within 2km are yellow, and more than 2km are red.

I actually did a map like this on Friday:
http://londonconnections.blogspot.co...ndon-gaps.html

I posted a similar, but much less pretty, map, a few months ago. Can't
find it now - i think i must have deleted it. Oh well.

But i want an actual readout of polygons, with lists of bounding stations
and exact areas. My OCD requires this. Then i need a map and/or dataset
showing the population density across London.

If you did want to do it with pure graphics, the best way i can think of
would be to do a Voronoi tesselation (using some code off the internet or
something [1]), split the regions into triangles centred on the stations,
then make postscript of the triangles with a graduated fill getting
darker/redder/etc as it goes out from the station [2]. That would look
pretty sweet.

I loaded all the station locations into a MySQL database, then wrote a
PHP script to generate an SVG file. I didn't bother calculating
distances - it just does separate passes to make the quarter mile discs
appear on top of the half mile discs, which achieves a similar effect.

The thing that excites me most is that you have the coordinates of all the
stations from Google Earth dudes - i've been using Clive's grid references
for tube stations and manually adding them for railway stations, which is
very tedious. I will be obtaining the dataset you used forthwith!

tom

[1] Such as:

http://www.qhull.org/

[2] Like so:

http://redgrittybrick.org/postscript/gradient.html

--
Science which is distinguishable from magic is insufficiently advanced