1. A method comprising: storing, at a server computer, a plurality of layers corresponding to a map of a geographic area, wherein the plurality of layers includes at least a first layer specifying a first class of roads and a second layer specifying a second class of roads; receiving, from a remote computer over a network, a request for map data corresponding to the map, wherein the request for the map data indicates a portion of the map that is to be rendered; and in response to the request, transmitting, to the remote computer over the network, at least the first layer and the second layer, wherein the first layer and the second layer are in a format that is usable by the remote computer to render, without receipt of additional map data, both the portion of the map and a zoomed version of the portion of the map, and wherein the zoomed version of the portion of the map includes additional map details based on the second class of roads.