Tutorial: Spatial Analysis of Accessibility of Wells using Map Algebra

1. Introduction

With map algebra we can do calculations with raster layers. This is useful for spatial analysis. For example, when we need to evaluate different criteria to find suitable or unsuitable locations we can use map algebra.

After this lesson you will be able to:

  • apply map algebra for raster analysis
  • distinguish Boolean, discrete, and continuous rasters
  • make legends for Boolean, discrete, and continuous maps
  • understand the use of Nodata
  • use logical operators
  • calculate distances from rasters
  • reclassify rasters
  • convert raster to vector points
  • sample raster values with vector points

In this lesson we'll address the following case.
The municipality of the (imaginary) oasis Aïn Kju Dzjis has hired you to analyse which wells are unsuitable for its inhabitants based on the following conditions:

Condition 1:
    The wells should be within 150 meters of houses or roads.

Condition 2:
    No industry, mine, or landfill within 300 meters of the wells.

Condition 3:
    The wells should be less than 40 meters deep.

You will use map algebra to perform the required analysis.

This lesson will follow this workflow:

Flowchart map algebra

The raster layers for this lesson can be downloaded from the main lesson page.