Spatial Analysis of Accessibility of Wells using Map Algebra
In this tutorial we'll apply map algebra to determine the accessibilty of wells. This tutorial was developed together with Kurt Menke (Bird's Eye View GIS).
5. Condition 3: Wells Less than 40 Meters Deep
For the last condition we need to identify the wells that are less than 40 m deep.
The gwlevel
layer gives the absolute elevation of the groundwater level in the well
in meters above sea level. In order to calculate the depth to the
groundwater, we need to subtract this from the surface elevation given
in the digital terrain model (DTM).
1. Open the Raster Calculator.
2. Subtract the absolute well depth from the DTM using this calculation: dtm@1 - gwlevel@1. Call the output layer welldepth.tif.
3. Style the welldepth layer with the appropriate renderer for this raster type.
4. Next, calculate in the Raster Calculator a Boolean map with wells less than 40 m deep. Call the output layer notdeep.tif.
5. Style the notdeep layer.
