“Raster analysis are operations performed to alter the cell values of the raw data. The output are a result of computations on a cell-by-cell basis. The value of the output for one cell is usually ind”
In this module, we explore the raster operations namely zonal operations. We explore how zonal analysis can be achieved in QGIS.
Goal: You are a disaster manager in your region and you are required to produce a map which shows the population density of each administrative area.
Data: appendix3-local-data - kzn_pop_count.tif,districts.shp
Name | Expectation |
---|---|
Data |
appendix3-local-data - kzn_pop_count.tif,districts.shp |
CRS |
EPSG:3857 |
Spatial algorithm |
Zonal Statistics |
Column attribute |
density,Decimal size 10,precision 6 |
Raster operations are grouped into three types:
Raster operations are cell by cell computations. Zonal operations work within groups of cells. The zones may be contiguous or non-contiguous. Contiguous zones include cells that are spatially connected, whilst a non-contiguous zone includes separate regions of cells. When undertaking zonal operations the zones can be defined as a raster or vector. When using a raster as a zone all the cells with the same value would define the zone and for polygons all the features with the same attribute.
Zonal operations can be done on single raster or multi rasters. An example of a zone can be a census district and the zonal statistics cane counting the number of streams that occur in each census district.