A map server generates vector descriptors in a non-raster format, each indicating a geometry of a respective map element, to render a first map image of a selected geographic region at a client device. The map server then provides the vector descriptors to the client device. Upon receiving an indication that a second map image for the selected geographic region is to be rendered at the client device, the map server generates 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 provides the modification indication to the client device, so that the client device can render the second map image using at least some of the vector descriptors and the modification indication.