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Operations:
- Slope: DEM Layer.tif=[QGIS/Raster Based Terrain Analysis]=>slope.tif=>[r.in.gdal]=>slope
- Grid: [QGIS/Vector/Research Tools/Vector Grid]=>grid.shp=[v.in.ogr]=>grid=>[v.to.rast]=>grid
- Crossing Grid and Slope: grid*slope=[r.average]=>gridSlope=[r.to.vect]=>gridSlope=[v.out.ogr]=>gridSlope.shp
Open your DEM Layer
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Here, we applied a pseudo-color table
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Slope Raster creation
First, create a slope map using raster-based Terrain Raster Analysis Plugin
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Import your raster
Use r.in.gdal
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Vector Grid Creation
Create a grid covering your area of interest
Vector > Research Tools > Vector Grid
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It generates a grid shapefile with an ID Colum which is unique
Here, the grid covers the slope map
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Import your grid
v.in.ogr
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Rasterize your grid using ID Column
v.to.rast.attr
The ID attribute will become the cell's category
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Set the region on your rasterized vector grid
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Generate an average slope grid using the two existing rasters
r.average
" r.average - Finds the average of values in a cover map within areas assigned the same category value in a user-specified base map. "
Remember that each square area of the rasterized vector grid has a unique category as it corresponds to the previous ID attribute of the vector grid
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Vectorize your average slope grid
r.to.vect.area
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Here, we labeled the generated vector using the cat column. Each number represents the average slope in each cell.
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Export it to shapeFile (optional)
v.out.ogr
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Remarks:
Slope could have been created using r.slope.aspect within GRASS instead of using QGIS plugin
You could apply the same procudure using features instead of a grid. For example, you could get the average slope touching and/or surrounding some urban areas in the context of a Terrain Movement study
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