Slope mapping is a data presentation that emphasizes steep gradient zones instead of the usual highs and lows. Slope maps express the maximum "slope," or maximum horizontal rate of change, in the data at a given point. This new emphasis on the slope often discloses important geologic information that was hidden or obscured on normal map presentations. Slope mapping of gravity and magnetic data has revealed the locations of major density and magnetization boundaries in the earth's crust. Theoretical studies and empirical work suggest that these same boundaries have considerable exploration importance.

Manual, computer, and analog techniques are available for performing the slope-map operation. The manual technique uses hand-measured slope values and hand contouring to produce usually adequate--if not precise--slope maps over large areas. The computer-implemented method uses uniformly gridded input map data to produce accurate slope maps over limited areas. The analog method uses the Datacolor machine to make instantaneous and reasonably accurate video presentations of colored slope maps from suitable "normal" contour maps.