LIDAR

http://www.loc.gov/exhibits/911/911-maps.html

The image above is an example of LIDAR mapping.  This LIDAR image shows the different levels elevation of the buildings of ground zero site in New York.  The 3d mapping was useful for fire rescue and emergency response units because the laser technology provides information like changes in the pile of rubble to make sure it was safe.  The color blue in the image has the highest elevation and as elevation drops the colors change to green, yellow, orange, to red being the ground floor.