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How Does Google Get Accurate Geoinformation for Google Maps?


Have you ever wondered how Google Maps manages to have reasonably accurate map data for so much of the world? I ran across an interesting video from Google’s I/O 2013 conference, about their Ground Truth project, which compiles and refines data from various authoritative sources to populate Google Maps.  The project has mapped 43 countries in the first five years, and is working to expand to new countries.

It’s a really enormous job. Think about having to keep track of which directions you can turn from each road into every road intersection in 43 different countries. For one thing, that’s obviously a lot of intersections. For another, it changes over time. So, the first two ingredients in Google’s magical formula for providing accurate map data are a huge number of people, and a truly massive collection of geoinformation.

With all of those the people and data, Google’s approach is to take the highest quality raw map data, and successively clean it up with satellite and aerial imagery, and their own Street View panoramic, street-level imagery. Most of this is done with Google’s own internal, homegrown, mapping tool, Atlas. In addition to providing an interface for manual corrections, Atlas also uses algorithms to automate certain tasks. For example, it has algorithms that check street names in the maps against street signs visible in Street View imagery.

The video briefly shows a really neat feature in Atlas (see minute 9:12) which starts with a top down view of an area, and then allows you to browse around that view with a fish-eye viewer showing Street View data under the location of the cursor. It’s hard to describe in words, but quite slick and intuitive when you see it.


Google’s internal, homegrown Atlas software provides the ability to see a fisheye-lens view of a particular location. The fisheye view shows Google’s Street View panoramic, street-level data. (Credit: Stephen Shankland/CNET)

I was also impressed by Google’s process of repeatedly revising previously mapped areas. An important source of updates is Google map users themselves, who are presented within the Google Maps interfaces with mechanisms for reporting mistakes. Google also has a browser-based product called Mapmaker that allows interested users to add their own map information, and make their own changes to Google’s maps. Changes made in this way are then moderated by Google staff to ensure that the changes conform to all Google policies. This is how Google Maps is able to provide data for 200 countries – far more than Google has addressed in their Ground Truth program.

If you ever use Google Maps and wonder how it all works, this video is worth a view.