Let's satisfy the first customer by showing the houses with correct aspect values. First of all, we need the SRTM DEM we downloaded and clipped to our study area, then transformed to our projection. If we load it, we can use GDAL's raster processing algorithms to do some terrain analysis. As QGIS does not have many tools dedicated to raster analysis, it uses external modules. This implies one very important specificity of raster analysis in QGIS--we cannot use memory layers. We have to save every intermediate result to disk. This is the case in calculating the aspect of our DEM, which you can do as follows:
- Open Raster | Terrain Analysis | Aspect from the menu bar.
- Select the clipped SRTM DEM as Elevation layer ...
