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While not a standard feature of topographic maps, for bushwalking purposes it can be very useful to be able to see slopes. If styled correctly, they can give an excellent primitive representation of cliffs in the area, enabling identification of possible passes and canyons.

Use the Raster Terrain Analysis → Slope tool in the Processing Toolbox, either on the DEM or the depressionless DEM.

It can be styled using a gradient style to aid in identification of passable/impassable areas.

Compressing large slope files

Because the Slope layer is just a style file on top of a (possibly very large) DEM, it can take up a lot of space when it comes to saving the files for use in QField.

Converting the DEM to a much simpler raster can save large amounts of space, and make using the data in a mobile device much more responsive.

From the Processing Toolbox, use the (GDAL) Raster Calculator - there is now also a native Raster Calculator - with the DEM (or depressionless DEM) as Input A, the output type as Int32, and the following formula in the Calculation box:

(A>40)*(A⇐50)*1 + (A>50)*(A⇐60)*2 + (A>60)*(A⇐70)*3 + (A>70)*4

The resulting calculated layer can be as little as 10% of the size of the original.

You need a slightly different style file to style this layer, but it should look identical in use.

qgis_slope.txt · Last modified: 2024/05/12 16:31 by bushwalking

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