By Charlie Frye, Esri Chief Cartographer
Using ArcMap to symbolize a hillshade raster layer (the output of the Spatial or 3D Analyst’s Hillshade tool) is pretty straightforward, and the default symbology (black to white ramp) doesn’t look too bad. In fact, if your hillshade layer is the only layer in your map, and if you don’t mind not seeing some of the details that have been visually absorbed into the darker tones, the default symbology is okay. To be fair, the default symbology for hillshades is useful for much more than just terrain depictions, so it’s good to know what might be helpful when depicting terrain with a hillshade. The image to the left is an example of a hillshade using the default color ramp.
In most cases a hillshade will not be the only layer in your map, so you need symbolize it so it works as the backdrop to other more critical information in the foreground of your map. Generally, as you add more information to your map, the lighter the darkest color of the hillshade should be. Here are some examples:
The dark gray color ramp in this image would work if only a few points and labels needed to be shown.
However, if more information is needs to be shown, then this light gray color ramp would allow that information to be seen more easily.
Both of the above color ramps are pure gray, i.e., no hue is shown, which can make your maps appear cold or less approachable than you may want. One trick to reduce that effect is to ‘warm up’ your hillshade by adding a tiny bit of red.
These color ramps are all in HillhadeColorRamps.style.
In fact, just by adding a little color, you can change the tone of your map. Below are a few examples (note: because they are side by side, the differences between them are accentuated.)
Another consideration for choosing how dark or light your hillshade needs to be is whether it will be used with a transparent layer. For instance you could draw, with transparency, elevation tint bands, soils polygons, or geologic unit polygons above a hillshade. In these cases it is typically desirable to have the lightest possible portrayal of your hillshade that still shows the terrain. The idea is that the information displayed on top of the hillshade is more important, and the hillshade is there to provide context. To that end, the HillhadeColorRamps.style contains normal, dark, and light versions of each hillshade, making it easy to select the one that makes the most sense for your map.
Finally, when using a hillshade in a map, you should change the interpolation method display from the default of Nearest Neighbor to Bilinear Interpolation. You will find this setting on the raster Layer Properties’ dialog display tab. The image below shows where to make the change:
The effect of changing the interpolation method is subtle, but important as some of the pixelated or hard edged appearance is removed.
Nearest neighbor interpolation (the default method), at the top, and Bilinear interpolation, at the bottom
All these images were created using a 3 meter resolution IfSAR elevation model from NOAA. The area depicted is the Crafton Hills, located just to the north and east of Esri and Redlands.