"In order to create these features, we rebuilt Maps using vector graphics to dynamically draw the map as you use it. Building a vector graphics engine capable of achieving the visual quality and performance level you expect from Google Maps was a major technical challenge and enables all sorts of future possibilities. So we wanted to give you a closer look under the hood at the technology driving the next generation of mobile maps.
". . . . Previously, Google Maps downloaded the map as sets of individual 256x256 pixel 'image tiles.'Each pre-rendered image tile was downloaded with its own section of map imagery, roads, labels and other features baked right in. Google Maps would download each tile as you needed it and then stitch sets together to form the map you see. It takes more than 360 billion tiles to cover the whole world at 20 zoom levels! Now, we use vector graphics to dynamically draw the map. Maps will download 'vector tiles' that describe the underlying geometry of the map. You can think of them as the blueprints needed to draw a map, instead of static map images. Because you only need to download the blueprints, the amount of data needed to draw maps from vector tiles is drastically less than when downloading pre-rendered image tiles. Google Maps isn’t the first mobile app to use vector graphics—in fact, Google Earth and our Navigation (Beta) feature do already. But a combination of modern device hardware and innovative engineering allow us to stream vector tiles efficiently and render them smoothly, while maintaining the speed and readability we require in Google Maps" (The Official Google Blog, 12-17-2010).