Practical GIS

Using zonal statistics

Although calculating statistics from a whole raster layer has its own advantages, now we need raster statistics from only the portions overlapping with our suitable areas. We can do this kind of calculation automatically by using zonal statistics. Zonal statistics require a raster layer and a polygon layer as inputs, then creates and fills up attribute columns with all kinds of statistical indices (like count, sum, average, standard deviation, and so on) in the output polygon layer. In order to calculate all the required statistics, we need all the input raster layers first:

1. Open every raster layer needed for the statistics--the water distance, the mean coordinate distance, the slope, and the suitability layers.