February 6, 2024

Easily Created Slope Maps in Global Mapper

Written by: Amanda Lind

Creating slope maps in Global Mapper can be as easy as changing a dropdown menu setting. Slope maps are often used in planning construction, trails, and more. They display the change in elevation of an area. Topographic maps use contour lines to communicate a similar idea, but a slope map displays slope values as a grid layer based on degrees or percent slope.

Slope maps in Global Mapper are made using elevation rasters. Are you creating a slope map from Contour lines? Grid it into a raster first using the Create Elevation Grid tool.

Displaying Elevation Data Based on Slope Values

Slope Shader

In Global Mapper, the display of elevation data can be used to communicate elevation values as well as slope values. To see the slope values in an elevation raster or grid layer, simply change the shader dropdown menu in the Analysis toolbar. Global Mapper will automatically calculate and display the slope value for each grid cell.

Tips:

To change the elevation legend from degrees to percentages, right-click on the legend and choose Elevation Legend Options.
The default colors are black and white, but that can be changed in the Configuration Menu under Shader Options. Read more about that in the next section.

A river DEM shaded in black and white representing slope values. — The Slope Shader changes the data display from elevation values to slope values.

Slope Direction Shader

Another built-in shader option is the Slope Direction Shader which displays the aspect of each slope in degrees. These screenshots were taken of the same data in the same location, however, they communicate different information about the terrain. The colors of the slope direction shader can be changed in the Configuration Menu under Shader Options.

A river DEM where is cell is shaded to represent the azimuth direction it's facing. — The Slope Direction shader colors the grid cells based on the azimuth direction they are facing.

Highlighting Specific Slopes

Customize the Existing Slope Shader

By default, the Slope Shader legend in the workspace displays the slope in black and white, and the listed minimum and maximum values are 2 standard deviations away from the mean. This means that the values listed at the top and bottom of the legend don’t necessarily include distant outliers, although they are still displayed on the map.

You can adjust the slope shader to use specific min/max values. All other values will be colored white. The Coloring Between Min and Max Slope Values option provides the ability to add a third color to the gradient in between the black and white. This is one method for visually highlighting the min/max values, though creating a custom shader provides more flexibility.

Creating a Custom Shader to Display Multiple Values

Custom Shaders in Global Mapper allow you to choose which values, or ranges of values, are assigned a color. You can color specific values while leaving the others as white, or create a gradient of values, as shown in the image below. In this example, the slope values are displayed 5 degrees apart in a gradient, highlighting the steepest slopes with the brightest color. Shadows are applied indiscriminately to the elevation layer as a whole based on settings in the hill shade tool.

A river DEm whee ths slope is displayed using a purple to yellow gradient. — This custom slope shader was created to highlight the steepest parts of the data.

A reiver DEM where all cells with a slope less than 5 degrees are shaded red, and the steeper slopes are white — This custom shader only colors slopes less than 5 degrees. The hillshade settings still add gray shadows for elevation context.

For step-by-step instructions on creating an elevation shader, check out this tutorial: How to Create a Custom Shader. When creating a slope shader be sure to check the box at the bottom of the dialog Shade Slope Values (Degrees) Rather than Elevations. This will change the provided values so they are treated as slope angles in degrees and allow you to setup shading based on the slope.

Learn more about all of Global Mapper’s shaders in this blog: Custom Shaders for Gridded Data in Global Mapper.

Creating Polygons from Sloped Areas

For some workflows, area features are necessary to outline areas of desired slope. The Vectorize Raster tool can be used to automatically create these area features. With the Slope Shader enabled in the workspace, the tool will automatically adjust to measure slope values instead of elevation.

All areas with slopes of less than 5 degrees are outlined with a generated area feature. — Polygons representing areas of less than 5 degrees of slope, and the settings used in the Vectorize Raster tool to create them.

To extract multiple values at once, First use the Raster Reclassify tool to break up the layer into sections based on slope. For a full demonstration of how to use both of these tools to create polygons, see this video tutorial: Extracting slopes in Global Mapper

Interested in changing the slopes in your data? Here is a selection of tools in Global Mapper that manipulate slopes in data:

Flattening Terrain Using Area Features
Create Flattened site plan
Terrain Paint
Adjust Elevations to a Single Slope (for vector features)

If you would like to explore creating slope maps in Global Mapper, download a 14-day free trial today! If you have any questions, please contact us.