Hillshade Testing

When I was putting together the map showing the Topography of the Caroni River Basin, I go up to speed on 3 important parameters when generating a Hillshade: Z Factor, Azimuth, and Angle. Here is a quick comparison of these factors.

The Z factor is used to exaggerate the vertical features of the terrain by multiplying the elevation values by the factor. The first image shows the comparison of different Z factors on the Caroni River basin terrain. The Z Factor of 1 shows the original values as they exist in the dataset. The changes in elevation are difficult to see, especially in the southern part of the watershed where there is less variation. As the Z factor is increased, these features become more prominent, but at the expense of losing detail in the Northern range as the hills begin to block the light source.

Azimuth refers to the sun’s position with respect to the subject. An azimuth of 0° means the sun is located to the north, 90° is to the east, 180° is to the south, and 270° is to the west. The 0° azimuth creates a lot of shadow south of the Northern Range, while the 180° illuminates it too much. The default azimuth is 315°, which is a north-west position of the sun.

Angle (or altitude) is the position of the sun above the Earth’s surface. A 0° angle means that the sun is on the horizon, so you can think of sunrise or sunset, when not much land is being illuminated. 90° means that the sun is directly overhead, which results in no shadows. The default angle is 45°, which is a nice balance of light and shadow.

The final map of the Caroni River Basin Topography uses the default azimuth of 315° and angle of 45°, while the Z factor is set to 5. It is worthwhile testing these parameters to see which combination best highlights the features you want your audience to notice.