Google has primary used two sources of data for their Google Maps product. Google announced in a Google Groups thread, that they are going to be sticking with just one source for the foreseeable future. That source is Tele Atlas.

Maps Guide Adam explained that Tele Atlas powered Google Maps API and Google Maps for Mobile fully and will now power Google Maps fully. Adam explains that you should see many improvements, but there may be some issues with some locations.

If you find issues, Google recommends two things to help improve the map tool:

(1) Use the community edit feature.
(2) Tell Tele Atlas of bugs or mistakes over here

Forum discussion at Google Groups.