In this tutorial, we will explore the methods for performing Contour and Terrain Analysis using Global Mapper. Whether you are a GIS professional or a beginner, understanding how to handle elevation data is crucial for spatial modeling.
It is worth noting that Global Mapper’s contour analysis output might differ slightly from traditional ESRI products (ArcGIS) or QGIS. If you are coming from those environments, the results may feel a bit unfamiliar at first, but Global Mapper offers a very intuitive and powerful workflow for terrain visualization.
1. Creating a DEM from Digital Topographic Maps
The first step in terrain analysis is generating a Digital Elevation Model (DEM) from vector contour data.
https://drive.google.com/file/d/1uXhyVSzw-kUuPyByJ2zwX7HlS-RVl2mh/view?usp=sharing
Opening the Data
To begin, you need to load your contour data (usually in .shp format). Go to:
File > Open Data File(s) (Shortcut: Ctrl+O)
Once the file is selected, the contours will be displayed on the main screen.
Adjusting Contour Visibility (Changing Line Styles)
Sometimes, the default contour colors are difficult to see against the background. To change the color for better visibility:
Open the Control Center.
Right-click on the contour layer and select Options... (or double-click the layer).
In the Vector Options window, navigate to the Line Styles tab.
Select the radio button for Use Same Style for All Features and click Select Style....
In the Select Line Style window, click the Color... button and choose a high-contrast color. Click OK to apply.
As shown below, the contours are now much clearer.
2. Generating the Elevation Grid (DEM)
Now that the data is loaded, we need to convert these vector lines into a continuous surface.
Assigning Elevation Attributes
Before creating the grid, you must tell Global Mapper which attribute contains the height data.
Right-click the layer in the Control Center > Options....
Go to the Elevations tab.
In the Get 'Elevations' From Attribute Value dropdown, select the field that represents height (usually 'CONT' for contours). Click Apply and OK.
Creating the Grid
Right-click the layer in the Control Center > Analysis > Grid (Create Elevation Grid from 3D Vector/Lidar Data...).
The Grid Creation Options window will appear. For basic analysis, you can simply click OK to use the default settings.
The DEM is now successfully generated.
3. Enhancing Visualization: Legends and Shaders
By default, the DEM appears as a grayscale gradient. To make it more informative, we can add a legend and change the color ramp.
Adding an Elevation Legend
Go to View > Workspace Layout Options > Elevation Legend....
In the Configuration window, set the following:
Units: Select Metric (meters).
Transparency: Set to 100% (Opaque).
Legend Range: Choose Data Extents to show the full range of your specific terrain (e.g., 65m to 135m).
Click Apply and OK.
The legend will now appear on your screen, indicating the elevation range of your terrain.
Changing the Color Ramp (Shaders)
Global Mapper provides various "Shaders" to visualize elevation.
Locate the Shader dropdown menu on the top toolbar (usually defaults to "Atlas Shader" or "Gradient Shader").
Select Atlas Shader for a traditional topographic map look (Green for lowlands, Red/Brown for highlands).
4. Terrain Distribution Analysis: Raster Reclassification
To understand the distribution of elevation—specifically, how much area each elevation range occupies—we use Raster Reclassification.
Go to Raster Analysis > Raster Reclassification....
In the Raster Reclassify window:
Input Layer: Select your generated Grid layer.
Number of Bins: Set how many categories you want to divide the terrain into (e.g., 15).
Labels/Colorize: Toggle these to display area values and colors.
Export to CSV: You can save this data to a spreadsheet for precise reporting.
Click Display in Graph Window to see a bar chart of the elevation distribution.
Note: While you cannot customize the font size in the built-in graph window, you can save the graph as an image or use the CSV data to create a custom chart in Excel.
5. Slope and Aspect Analysis
Global Mapper makes Slope (gradient) and Aspect (direction) analysis incredibly simple by utilizing the Shader system.
Slope Analysis
Change the Shader from "Atlas Shader" to Slope Shader.
The map will transform into a grayscale or colored representation of the terrain's steepness. You can then use the Raster Reclassification tool mentioned above to calculate the area for specific slope ranges.
Aspect (Slope Direction) Analysis
Select Slope Direction Shader from the dropdown.
This visualizes which direction the slopes are facing (North, South, etc.), which is vital for environmental and agricultural studies.
Conclusion
Today, we covered the essentials of terrain analysis in Global Mapper:
Converting contours to a DEM.
Customizing Legends and Shaders for better visualization.
Using Raster Reclassification to analyze elevation, slope, and aspect distribution.
By mastering these tools, you can extract meaningful geographic insights from simple topographic data. Stay tuned for more GIS tutorials!
Keywords: Global Mapper, Terrain Analysis, DEM Creation, GIS Tutorial, Raster Reclassification, Slope Analysis, Aspect Analysis, Digital Elevation Model.
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