QGIS User Guide - OSGeo Download Server

9.9 La barra strumenti GRASS
Contents, then check transparency of the colored gtopo30 layer. You should see that the 3D
effect stands out more strongly compared to the first shaded relief map.
Figura 41: Displaying shaded relief created with the GRASS module r.shaded.relief
Raster statistics in a vector map
The next example shows how a GRASS module can aggregate raster data and add columns of
statistics for each polygon in a vector map.
• Again using the Alaska data, refer to 9.4 to import the trees shapefile from the
vmap0_shapefiles directory into GRASS.
• Now an intermediary step is required: centroids must be added to the imported trees map to
make it a complete GRASS area vector (including both boundaries and centroids).
• From the toolbox choose Vector -> Manage features, and open the module v.centroids.
• Enter as the output vector map forest_areas and run the module.
• Now load the forest_areas vector and display the types of forests - deciduous, ever-
green, mixed - in different colors: In the layer Properties window, symbology tab, choo-
se Legend type Unique value and set the Classification field VEGDESC to VEGDESC.
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