How Google's Ground Truth maps the world (pictures)

Google spends a lot of time correcting data it receives, through a project called Ground Truth. Here, the left side shows the original data from the U.S. census program. At right is Google's corrected version.

The essence of the Ground Truth project is marrying Google's real-world information with data sets from sources such as cities, census operations, and postal address databases. "You can conflate those two together and correct one with the other," says Michael Weiss-Malik, engineering director for Google's Ground Truth and Map Maker.

In Atlas, yellow routes indicate the direction a car is entering an intersection. Green routes are permissible, and red routes are prohibited.

The Atlas tool lets Google Maps staffers hover over the map and see a fisheye-lens view of a particular point on a road. The bubble shows images taken with Street View.

With its Atlas tool, Google Maps staff can zoom into a Street View look at an intersection with Google's own graphical overlay of traffic restrictions.

In Google's Ground Truth project, trained operators use Google's internal Atlas software to map out a virtual version of the world. The software can show real-world signs for reference purposes.

Ground Truth combines geographic data with Google's own data to try to figure out what's actually happening in the real world.

Newer Ground Truth work involves mapping interiors such as the San Francisco Airport -- including routes through them. Buildings have triple the information density as roads, posing more processing challenges for Google.

Google's mapping tools recognize features in the real world such as street markings, traffic signs, and company logos.

The Google Maps team reviews complaints of inaccuracies from users with the Atlas tool. In this case, the problem is with a road that's under construction.

Ground Truth now is up and running in 43 countries. Once it's launched, Google must maintain the data, because maps go out of date constantly.

Another example of Google cleaning up and annotating inaccurate original data.

Part of the Ground Truth effort is correcting bad geographic data from sources such as governments. In cases where the data set is correct but distorted or shifted, Google can mathematically translate geographic items to new locations.

Google Maps employees carefully align road routes with satellite imagery using the Atlas software.