1. A geographic database stored on a computer readable medium for use with a navigation system, said geographic database comprising: data representing roads located in a geographic area, wherein the data representing roads includes data representing the road geometry, wherein the data representing the road geometry include a horizontal component and an altitudinal component, wherein the altitudinal component includes data defining straight line segments and vertical curves coinciding vertically with the represented portions of roads, and wherein said data representing roads may be used by said navigation system to provide a navigation-related feature, wherein said navigation-related feature includes at least one of: a map display, a route calculation, a route guidance, an adaptive cruise control and an adaptive lighting control.