1. A graphical mapping system configured to display mapping information on a handheld device, said system comprising: an image map database configured to store map data for a plurality of geographic areas, said map data being useful for generating graphical maps; a vector map database configured to store vector map data, said vector map data being useful for generating vector overlays that correspond to said graphical maps, said vector map data being selectively displayed on the handheld device based on a position of a cursor over said graphical map; a set of image congestion avoidance heuristics configured to dynamically optimize an amount of mapping information displayed on said handheld device based on a requested zoom level; and wherein a set of image mapping data and a corresponding set of vector mapping data, both associated with a given geographic location, are retrievable in response to a mapping request from the handheld device.