005] Global Mapper - Viewshed Analysis

Following our previous session, today we will dive into Viewshed Analysis.

Viewshed analysis is primarily used to identify changes in visible areas caused by specific projects or developments. It is an essential process in visual impact assessment, where you select major viewpoints and compare the "current state" versus the "planned state" to see how the landscape will change. (In practice, many only perform the current state analysis).

In the past, when performing viewshed analysis in software like QGIS or ArcView—especially when including buildings—you often had to convert building vector data into a DEM (Digital Elevation Model) and overlay it on the terrain. However, one of Global Mapper's greatest strengths is its ability to analyze building vector data directly without the need for DEM conversion. This feature has been available in Global Mapper for over 10 years, and it remains one of the most efficient ways to handle complex terrain data.

Let's get started.

Note: Modifying building attribute values is a separate task, so for today’s tutorial, we will focus solely on the terrain (topography).

First, please Load the Workspace we created in the last session.

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• File -> Load Workspace... (Ctrl+W)

If you have loaded the work from the previous session, your screen should look like the one below.

From the icon toolbar, select Create Viewshed (it looks like a lighthouse beam on top of a mountain).

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• Create Viewshed (Alt+V): Generate an area to display line-of-sight using loaded elevation grid data and user-defined source point location, height, and radius.

Once selected, a tip message will appear with instructions on how to start the analysis.

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• Tip: The Viewshed Tool allows registered users to perform a Viewshed analysis using loaded elevation grid data with a user-specified transmitter location, height, and radius... To perform a Viewshed analysis, press and release the left mouse button at the position where you wish to place the transmitter.

• Check: Don't Show This Again

• Button: OK

After clicking OK, your mouse cursor will change. (The cursor change isn't visible in the screenshot, but it will look different).

Click on the map at a location similar to the one shown below to set your observation point.

Once you click, the Viewshed Setup window will appear.

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• Layer Description: VP01 (Enter the name for the new layer)

• Transmitter Elevation: 1.6 METERS above Ground (Think of this as the observer's eye level).

• View Radius: 5 Kilometers (The maximum distance to analyze).

• Sample Spacing: X-axis: 25 meters, Y-axis: 25 meters (Controls precision; smaller values are more accurate but slower).

• View Angle:

  • Start Angle: 290

  • Swept Angle: 60

  • (Note: Starting at 290° and sweeping 60° clockwise means it analyzes from 290° to 350°).

• Earth Curvature: [X] Ignore Earth Curvature (Check this if you want to ignore the earth's curve).

• Obstructions from Vector Data:

  • [X] Use Vector Features with Heights

  • [X] Heights of Vector Features Relative to Ground

Key Parameter Explanations:

• Layer: This creates a new layer. Enter the desired name here.

• Transmitter Elevation: This is essentially the height of the observer's eyes. It will calculate visibility from 1.6m above the ground at the clicked point.

• View Angle: This sets the horizontal range of the analysis. Start Angle is where the analysis begins (azimuth), and Swept Angle is the total arc covered.

• Display Color: Choose the color for the visible areas.

• View Radius: The distance from the observer that the analysis will cover.

• Sample Spacing: This defines the cell size for the analysis. Naturally, smaller cells provide higher resolution but take longer to process.

• Use Vector Features with Heights: This allows the analysis to detect and account for vector elements (like buildings) that have height attributes.

Once configured, click OK.

There we go! The results are out.

If you wish to modify an existing viewshed analysis, simply right-click the viewshed layer in the Control Center, select Edit Viewshed Parameters and Recalculate, change the settings, and click OK.

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• Edit Viewshed Parameters and Recalculate

• Change Viewshed Coverage Color...

Since this is just a "taste" of what the software can do, I've kept things simple for now.

While we manually clicked a point today, you can also register specific viewpoint data as a layer and analyze dozens of points simultaneously. You can overlap visible areas to determine "visibility frequency," or import building data with height attributes to perform a more realistic analysis. While it might not replace a full 3D viewshed simulation in every case, for standard reporting and professional visualization, there is nothing more convenient than this.

I assume those searching for "Global Mapper" and landing here are likely already familiar with at least one other GIS tool. I am trying to keep these tutorials concise so you can easily compare these features with the tools you currently use.

The autumn leaves are moving up toward the mountain ridges. I should grab my old camera and follow them.

That’s all for today!