In this example we find flatter areas in terrain that are suitable for airports, better farm land, or for hobbies like falconing. We import an SRTM file and create a map using Bing Streets as a background layer. With a few clicks we then create a Slope layer from the terrain elevation layer and then we color the Slope layer so that regions with slope less than 5 degrees are transparent, allowing the underlying base map to show through in "flat" regions. This topic uses Manifold Release 9 running in Windows 11.
This is the user manual topic version of the 5 Minute Tutorial - Find Flatter Areas in Terrain video. The video uses Manifold Viewer, the free, read-only version of Manifold Release 9
We have previously downloaded an SRTM terrain elevation file covering parts of Oregon, Idaho, California, and Nevada from the CGIAR SRTM Download Manager website.
The file is a 70MB GeoTIFF file. Import it into Manifold by dragging and dropping the .tif file from Windows Explorer into the Project pane.
That creates a new image and the image's table in the Project.
To create a map, in the Project pane we Right-click onto the image and choose Create - New Map.
In the New Map dialog we choose Bing streets as the Base layer and then we press Create Map.
A new Map component appears in the Project pane. We open the map by double-clicking the new Map component.
The component opens with two layers, one with the image showing the SRTM data and the other layer the Bing streets base layer. The SRTM layer appears with default, very low contrast styling. We could easily alter that using the Style dialog to provide a better terrain elevation display, but for the purposes of this topic we do not need to do that, as we will go straight to creating a slope layer.
We click on the Transform pane tab. We choose the SRTM layer as the subject of the Transform pane, and in the list of available templates we double-click on the Slope template.
We configure the Slope template as seen above. If we would like somewhat better accuracy, we could increase the Radius to 2 or even to 3. If we have a GPGPU capable GPU installed, the computation will still be very fast.
We have configured the template to save the results to a new image and table, called Slope. The default table name created automatically as we enter a name for the New image ends in ...Table. This topic uses a table name that ends in ...Tiles, which is how some users prefer to name tables for images. Others prefer to have all of their tables, both for drawings and images, end in ...Table. We can adjust the name automatically created for the table however we like.
Press Transform. That creates a new image called Slope along with the image's table in the Project pane.
Drag and drop the new image into the Map. The image appears with default styling.
We click on the Style pane layer, and configure the Style pane as seen above. Press the Update Style button and the map window will update to use the new style. In the illustration above, we have double-clicked the SRTM layer to turn that off.
We have used the Style pane to color the Slope layer so all regions with a slope under five degrees are transparent in the Slope image. We reckon that a slope of five degrees or less is "flat" enough for our purposes. If we preferred some value of slope other than five degrees to be the limit of what we considered "flat," we could simply edit the 5 interval to use a different number, such as 3.
Using transparency to color pixels that are five degrees or less in slope allows the background map to be seen through the transparent regions.
Zooming in, we can see how the background map is visible in regions of flatter terrain. At a glance, we can see the flatter areas in the region of interest.
If we like, we can add a Bing satellite layer to the map, so we can use either satellite photography or the street map to see what is located in flatter areas.
5 Minute Tutorial - Find Flatter Areas in Terrain
File - Create - New Data Source
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