Lasers were fired at the town from the ground and from the air to capture the height of buildings, trees and other features, using a technique called Lidar. Adding information from aerial photos and traditional surveys produced a full-colour 3D map, built up from more than 700 million points. The map is accurate to 4 centimetres in x, y and z - by comparison 3D structures in Google Earth are accurate to about 15 metres. "It's almost what you'd see if you flew around the area," says Hart. See a video of the map, above.