opengeos--geolibre/docs/tutorials/terrain-analysis.md

Terrain Analysis

This tutorial derives terrain products from a digital elevation model (DEM): a hillshade, a slope map, and contour lines. It uses the Raster tools under Processing → Raster.

!!! note "Desktop app required" The raster tools run on the rasterio Python sidecar, which the desktop app manages. They are not available in the browser build. See Getting Started.

1. Load a DEM

Add an elevation raster as a layer, for example a GeoTIFF or COG DEM (see Adding Data). The raster tools take a file path in and write a file path out, so a local or accessible raster works best.

2. Hillshade

1. Open Processing → Raster → Hillshade.
2. Choose the DEM as input and set the azimuth, altitude, and z-factor if you want to adjust the lighting.
3. Run it. The shaded-relief raster is added to the map. Place it under your other layers and lower their opacity for a relief backdrop.

3. Slope and aspect

• Processing → Raster → Slope computes steepness from the DEM.
• Processing → Raster → Aspect computes the compass direction of the steepest slope.

Run either against the DEM and style the output with a colormap. Open the Colorbar from the Controls menu to show the value scale.

4. Contours

1. Open Processing → Raster → Contour.
2. Choose the DEM and set the contour interval (the elevation difference between lines).
3. Run it to generate contour lines as a vector layer, which you can label and style like any vector data.

5. Clip to an area of interest

To restrict outputs to a study area, use Processing → Raster → Clip by extent (a bounding box) or Clip by mask layer (a vector mask). See Processing Tools.

Next steps

• Convert raster outputs to vectors with Polygonize, or write a Raster to COG for sharing. See Cloud-Native Data.
• Animate a time series of rasters with the Time Slider plugin. See Data Integrations.