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LULC QGIS Zonal Stats Tutorial#

You can easily derive insights about your area of interest from a Land Use Land Cover (LULC) map with just a few lines of code, or a few steps using GIS software.

This tutorial demonstrates how to calculate the percentage of each class type over any area of interest (AOI) from an Impact Observatory LULC map.

Requirements#

  • A Land Use Land Cover (LULC) GeoTIFF
    • Note that the GeoTIFF must be clipped to the boundary of your area of interest (AOI).
    • If your GeoTIFF includes areas where you do not want to count the pixels, you need to clip those areas out using a vector file.
    • See Projection Notes for more information on projections for statistics and visual appearance.
  • QGIS -- This tutorial uses QGIS, but ArcGIS Online, ArcGIS Pro, or the GDAL library can be used to achieve similar results.
  • Spreadsheet -- Google Sheets, Microsoft Excel, other

Outputs#

  • Pixel counts for LULC class over the AOI
  • Percent of each class throughout the AOI
  • A table, donut chart, and/or histogram of the results

Calculating Class Percentages#

Open data in QGIS#

Open the GeoTIFF in QGIS.

This tutorial can be used to analyze any of the three output GeoTIFFs from the IO Monitor. The example below shows a LULC map clipped to the extent of Miaoli County, Taiwan in QGIS for the 90-day date range 2022-11-01 to 2023-02-01.

Raster Layer Unique Values Report#

  • In QGIS, open the Processing Toolbox → Raster analysis → Raster layer unique values report.
  • In the pop-up window, select your GeoTIFF for the Input layer.
  • Optional: specify a location to save the report and a table format of the report using the button with three dots next to “Unique values report [optional]” and “Unique values table [optional].” If you do not specify a location your output will be saved to a temporary file, which is recommended.

This is a sample image of the raster layer unique values in QGIS.

  • Click Run

After the statistics are complete, another pop-up window will appear like the one below. Click on the file path.

This is a sample image of the unique values report in QGIS.

Clicking on the file path will open a page in your browser with the unique values report.

This is a sample image of the unique values report output in QGIS.

Creating a report in a Spreadsheet#

Copy and paste the values from the unique values report into a spreadsheet to conduct additional analysis. Use this Google Sheets Zonal Statistics Example as a template for your report (make sure when pasting to right click → “paste values only” to keep the table format of the data). You can also follow the tutorial below to create your style of report.

This is a sample image of the unique values html output in QGIS.

Understanding the Results#

Each pixel value aligns with the 9 LULC classes. Note that the values of 3 and 6 do not exist in any LULC maps from IO Monitor because these values have been combined into the rangeland class. Also note that most places will not have any snow/ice, or pixel values of 9 unless snow/ice is permanent.