Terrain
The Terrain toolbox turns a digital elevation model into everything you can read from the shape of the ground: how steep it is, which way it faces, whether it is smooth or broken, what kind of landform each place belongs to, and what can be seen from where.
Its 99 tools come from the Whitebox analysis suite and run entirely in your browser. Nearly all of them take one raster elevation model as input and return a new raster, which lands on your map as a layer you can style.
Getting an elevation model
Section titled “Getting an elevation model”Load a DEM through Add Data like any other raster, from a file on your computer or from a public source. The quality of everything below depends on it: a 30 metre global model shows valleys and ridges, not field margins, and a model built from photogrammetry carries buildings and trees on top of the ground rather than the ground itself.
Once loaded, the DEM appears in the input list of every Terrain tool.
The sub toolboxes
Section titled “The sub toolboxes”| Sub toolbox | What it is for | Tools |
|---|---|---|
| General | Shaded relief, smoothing, void filling, ridges and profiles. The everyday tools. | 36 |
| Derivatives | Slope, aspect and the full family of curvatures. | 23 |
| Landform Indices | Classify each cell as ridge, slope, valley or pit. | 7 |
| Multiscale Signatures | Measure the same property across many neighbourhood sizes at once. | 15 |
| Roughness & Texture | Quantify how broken or smooth the surface is. | 6 |
| Visibility | Viewsheds, sky view, openness, shadows and daylight. | 11 |
| Workflow Products | A finished pseudo 3D rendering in one run. | 1 |
Where to start
Section titled “Where to start”If you have never used this toolbox, three tools cover most needs.
Hillshade, in General, gives you the shaded relief image that makes any map readable. Run it once, put it under your other layers, and the terrain appears.
Slope, in Derivatives, gives you steepness in degrees or percent. It feeds everything from erosion risk to accessibility.
Aspect, also in Derivatives, gives the compass direction each slope faces, which drives sunlight, snow melt and vegetation.
The z factor
Section titled “The z factor”Most tools here offer a z factor, and it exists for one reason: the vertical unit of your DEM has to match its horizontal unit.
Leave it at 1 when both are metres, which is the usual case for a projected DEM. Set it when they differ, typically for a DEM in geographic coordinates, where horizontal distances are in degrees and heights in metres. A wrong z factor does not produce an error, it produces a slope map with plausible looking but meaningless values, so it is worth a moment of attention.
Everything is a raster. Each tool writes a new raster layer. Style it in Style to read it, since a fresh slope raster in grey levels rarely shows what you are after.
HTML reports. A few tools produce a report or a plot rather than a layer. Those are downloaded to your computer instead of being added to the map.
Size. The computation happens in your browser’s memory, so clip large models to your area of interest before running heavy multiscale analysis.
Credits
Section titled “Credits”These tools come from WhiteboxTools by Prof. John Lindsay, University of Guelph, whose manual documents each algorithm and the research it implements.