003] Global Mapper - Terrain Analysis, DEM Creation, and Raster Reclassification
Today, we will explore how to perform contour and terrain analysis using Global Mapper. If you are accustomed to ESRI products or Q-GIS, you might find Global Mapper's output slightly different at first, but its intuitive workflow is incredibly powerful once you get used to it.
"Before we begin, if you missed the previous session, check it out here:"
001] Global Mapper - Creating DEMs
1. Creating a DEM Using Digital Topographic Maps
The first step in terrain analysis is generating a Digital Elevation Model (DEM) from contour data. You can use your own data or any standard digital topographic map files.
download Terrain_data.zip (This is a safe proprietary data file for Global Mapper.)
Opening the Data
To begin, open your contour file in Global Mapper by navigating to File > Open Data File(s).
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| Global Mapper File Open menu screen |
Once the file is loaded, you will see the contour lines displayed on the screen. However, the default colors might not be very visible depending on your workspace settings.
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| Loaded contour lines on the main workspace |
Adjusting Contour Line Styles
To make the analysis easier, let's change the color of the contour lines. In the Control Center, select the contour layer, right-click, and choose Options.
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| Control Center layer options menu |
In the Vector Options window, go to the Line Styles tab and click on Select Style.
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| Vector Options - Line Styles tab |
From the Select Line Style window, click on Color, choose a highly visible color (like dark grey or black), and click OK to apply the changes.
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| Color picker and line style selection window |
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| Applying the new line style settings |
Now the contour lines are much clearer and easier to work with.
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| Map view with updated contour line colors |
2. Generating the Elevation Grid (DEM)
Now that we have our vector data, we need to convert it into a grid (DEM). The most critical step here is assigning the elevation attribute.
Assigning Elevation Attributes
Right-click the layer in the Control Center > Options > Elevations. Select the attribute field that contains the elevation data (usually 'CONT') and click Apply.
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| Assigning elevation attribute from the CONT field |
Creating the Grid
Next, right-click the layer again, and navigate to Analysis > Create Elevation Grid.
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| Accessing the Create Elevation Grid menu |
The Grid Creation Options window will appear. For basic analysis, you can simply click OK with the default settings.
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| Grid Creation Options window |
A DEM is now generated, showing the terrain as a black-and-white gradient by default.
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| Generated DEM in black and white gradient |
3. Adding an Elevation Legend
To understand the elevation range, we should add a legend to the screen. Go to View > Workspace Layout Options > Elevation Legend.
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| Workspace Layout Options menu for Elevation Legend |
In the Configuration window, set it as follows:
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| Elevation Legend configuration settings |
- Unit: Select Metric (meters) for standard measurements.
- Transparency: Set to Opaque (100%) for better visibility.
- Legend Range: Choose Data Extents to show the full range of your terrain.
Now a legend appears on the left, showing that our terrain ranges from 65m to 135m.
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| DEM with the elevation legend displayed |
4. Changing the Color Ramp (Shader)
While black-and-white is functional, most people prefer the standard topographic color scheme (red for high, blue for low). Global Mapper provides various pre-set Shaders.
On the top toolbar, click the drop-down menu next to the mountain icon (Shader list) and select Atlas Shader.
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| Selection of Atlas Shader from the drop-down menu |
The map now displays a more familiar topographic color scheme.
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| DEM with Atlas Shader applied |
5. Raster Reclassification and Statistics
If you need to know the exact area occupied by specific elevation ranges, use Raster Reclassification. Navigate to Raster Analysis > Raster Reclassification.
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| Raster Analysis - Raster Reclassification menu |
In the reclassification window, you can set the Number of Bins (how many levels to divide the data into) and see the area distribution in a bar graph.
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| Raster Reclassification setup and bar graph |
By clicking Display in Graph Window, you can view the distribution in a larger window and save it as an image or export the data as a CSV file for use in Excel.
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| Enlarged elevation distribution graph |
6. Slope and Aspect Analysis
Performing Slope (gradient) and Aspect (slope direction) analysis is just as simple. You only need to switch the Shader.
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| Selecting Slope Shader from the list |
Once you change the shader, the map updates instantly to show the slope distribution.
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| Slope analysis map output |
Conclusion
Global Mapper makes terrain analysis intuitive and fast. Whether you are generating a DEM or conducting advanced slope studies, the key lies in mastering the Shader options and Raster Analysis tools. Give it a try with your own topographic data!
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