Thursday, April 21, 2005

Make your own transit map with Google Maps

Google Maps continues to show what can be done with a few scripts, Photoshop and the satellite map view. Adrian Holovaty has created a how-to for people wanting to combine a city transit map with Google Maps.

Here's his
"How I did it":
  • Downloaded the CTA's official maps and combined them into a single image in Photoshop.
  • Downloaded a bunch of Google map tile images for reference, noting the coordinates in their URLs (example), and spliced them together.
  • Stretched and skewed the CTA map so that it was aligned as closely as possible to the Google map. This was the most time-consuming part of the process, and it didn't turn out as perfect as I'd have liked. I blame it on the CTA map designers for not being precise enough. :-)
  • Chopped the aligned CTA map into 128-by-128-pixel tiles that matched their corresponding Google map tiles exactly -- by size, shape and coordinates.
  • Wrote a server-side Python script that handles dispatching images. (Ideally a future version of the Greasemonkey script would embed the map images in itself directly.)
  • Wrote the Greasemonkey script that brings it all together.
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