Ask A Cartographer

Generalized Hillshade

April 29 2009 | 0 comments
Categories: Symbology

I've been playing around with the hillshade toolbox quite a bit lately, and have also been following the Mapping Center blog quite regularly.

I'm trying to create a locus map (to accompany a larger DEM-hillshade combo) which depicts the major terrain features of my state, much like you'd see in a physiographic map depicting major geographic features of an area exaggerating but at the same time generalizing those major features. Do you have any advice on how to accomplish this?

Mapping Center Answer:

To generalize the hillshade, use Focal Statistics, which is one of the same steps as in the Swiss hillshade model. In fact, it creates one of the outputs of the model, so you may already have created this. However, you can change some of the parameters, like the neighborhood type and size or the type of statistic used to see if you get something closer to what you are looking for. (The Swiss hillshade model uses a 4x4 rectangular neighborhood and a median statistic.)

Before you click OK to run the tool, use the Z factor to exaggerate the features. The question then becomes, how much do you exaggerate the features. In the Map Use book, we offer this:

"A vertical exaggeration between 2 and 3 is common with large scale oblique perspective maps, while a 50 to 1 exaggeration is often used for small scale maps of states or countries." Compare this with: "In practice, a vertical exaggeration of about 20 to 1 is typical on relief globes of a 60 centimeter (24 inch) diameter."

If you would like to post a comment, please login.

Contact Us | Legal | Privacy |