We told you earlier in the week how the Google Maps data is not always 100% accurate. Google does, however, put in an extraordinary amount effort into making it the best it can be.
Google originally depended largely on external data providers for its maps information. But that changed in 2008 when project Ground Truth was founded. The Ground Truth project involves getting data from authoritative sources such as governments, postal services and map providers, which is then overlayed on satellite imagery and updated to make it more accurate. Google then uses satellite imagery and Street View imagery to add a lot more data to the map. It uses a variety of processes including a lot of manual editing by highly trained map editors, as well as a number of algorithmic methods, such as using computer vision to go through Street View imagery and pick out street signs, street names, business logos and more. Finally, they get feed back from users via the ‘Report a problem’ feature, or Google Map Maker.
It is important to realize that there is a lot more to maps than what you see directly in Google Maps. Google Maps also contains a lot of hidden information such as road rules, including speed limits, one way streets, traffic lights, stop/yield signs and no turn signs. These are used by Google maps when providing directions.
Google Maps contains a lot more than just street names.
The Ground Truth project is not yet used for the whole world, but they have been expanding rapidly. Ground Truth recently announced their 50th country. For the remaining countries they use a combination of external data providers and Google Map Maker.
For a more in depth look at the Ground Truth project watch this excellent presentation from Google I/O 2013 and read a four part series on the making of maps on the Google Lat Long Blog. (Part 1, Part 2, Part 3, Part 4)