Expand Colormaps to include negative values for DEM display

Idea created by kimerlia on May 21, 2010
    The Colormap function appears to have been developed to create .gif image and similar color look-up tables. A very nice feature of the ArcMap implementation, however, is that RGB color values can be assigned to any positive integer in the range of unsigned short integers. This allows a continuous color ramp to be created for DEMs with all positive elevations, such as GLOBE DEM data. A major improvement would be to extend the Colormap function to include negative values within the range of signed short integers (-32767 to 32768). This would allow color ramps to be developed for all NGDC ETOPO dems, Coastal Relief Model dems and many more models with ocean depths and negative land elevations.

    The workaround I developed recently was to use the Map Algebra function to add the minimum elelvation ( the greatest negative sea depth in the map area) to all DEM values, creating a new DEM with all positive values. I could then create a Colormap with the 0 entry having the RGB color for the deepest ocean elevation, and so on. Below you will see a map of Puerto Rico and vicinity that I made with this Colomap, along with hillshading. Having the Colormap function simply being a list of negative to positive elevation value and associated RGB color values would have made this tedious workaround unnecessary.