1. A method in a map server for providing map data to a client device via a communication network, the method comprising: receiving from the client device, a request for map data corresponding to a specified geographic region; generating a first plurality of vector descriptors for rendering and displaying, at the client device, a first map image for the specified geographic region at a certain zoom level, wherein each vector descriptor indicates a geometry of a respective map element in accordance with a vector graphics format, and wherein each map element illustrates a respective physical entity in the geographic region; causing the first plurality of vector descriptors to be transmitted to the client device via the communication network; receiving an indication that a second map image for the same selected geographic region at the same certain zoom level to be rendered at the client device, wherein the second map image is different from the first map image, and wherein the second map image corresponds to a second plurality of vector descriptors; determining, at the map server, a difference between the first plurality of vector descriptors and the second plurality of vector descriptors, wherein one or more vector descriptors is included in each of the first plurality of vector descriptors and the second plurality of vector descriptors; based on the determined difference, generating a modification indication that indicates a set of one or more vector descriptors, each of which corresponds to a respective map element that is rendered in one but not both of the first map image and the second map image; and causing the modification indication to be transmitted to the client device via the communication network for rendering and displaying the second map image using at least some of the first plurality of vector descriptors and the modification indication.