Looking at the Google Transit overview map puzzles me:
Is the green colour supposed to mean anything? Participating organisations? If so, how?
The green areas are defined clickable regions on the map. In the United States and Canada, they are closely aligned to state and province borders. In other parts of the world they follow country borders. When I click on one of the green regions, the map shows a list of participating transit providers in that particular region.
The regions are polygons defined in the file http://www.google.com/intl/en/landing/transit/js/transit.data.js
The code that draws the map is in the file http://www.google.com/intl/en/landing/transit/js/transit.map.js
Note that the green polygons will not show in Internet Explorer. From