1. A computer implemented method of operating a navigation system to provide road curvature comprising: obtaining, using a processor, a plurality of spline control points representing a two-dimensional geometry of a portion of a road segment from a geographic database associated with said navigation system, wherein each of the spline control points lies on or close to a point along the represented road segment, wherein each of the spline control points comprises a latitude and longitude coordinate pair; obtaining, using the processor, data indicating a road grade of said portion of said road segment from said geographic database; and projecting, using the processor, said spline control points onto a slope plane having a slope provided by said road grade to obtain a plurality of projected spline control points, wherein the projected spline control points provide a representation of a restored true road curvature of said portion of said road segment that restores altitude components to the road curvature, wherein each of the projected spline control points comprise a latitude, longitude and altitude coordinate triple.