How Google maps the world
Type "77 Massachusetts Avenue 02139" into Google Earth, and you'll see MIT's Great Dome in all its glory. Click a button to zoom out, and soon you'll see the state capitol, the celebrated Zakim Bridge, and maybe some other college up the river. These images, which are shared by Google Maps, are actually a combination of aerial photos and satellite imagery--and a lot of postprocessing. Technology Review interviewed engineers at Google and at DigitalGlobe, the company that supplies Google's satellite photos, and did a little bit of reverse-engineering to figure out how it works. Credit: Bryan Christie 1. High-Resolution Imagery As it passes overhead at an altitude of 450 kilometers, DigitalGlobe's QuickBird satellite photographs the planet's surface. The satellite can take "snapshots" roughly 16.5 kilometers square or record "strips," which measure 16.5 by 330 kilometers. The average resolution is roughly 60 square centimeters pe