US Patent 8243102 Derivative-based selection of zones for banded map display

A graphics or image rendering system, such as a map image rendering system, determines a viewing window of a map surface to be displayed, wherein the viewing plane is at an angle of incidence with respect to the map surface. The method generally determines a depth boundary along the map surface where a height projection of a depth increment of a first unit of area is lower than a threshold height increment at a non-zero angle of incidence and at a single zoom level magnification. The method renders the first unit of area within the depth boundary and a second unit of area outside the depth boundary. The first unit of area is rendered at a first density of map data and the second unit of area is rendered at a second density of map data that is lower than the first density of map data.