Land cover & land change

Land cover rasters and how they change: NLCD and ESA WorldCover downloads, change matrices, urban growth, impervious surface, class areas and categorical raster pitfalls.

Williamson County, Texas, on a coarse grid of NLCD land cover classes in 2001 and 2021, with developed land in red spreading between them. the same county, twenty years apart20012021Williamson County, Texas: developed land 332 km² in 2001, 523 km² in 2021 (NLCD)

A land cover map turns every pixel into a class: water, forest, cropland, four intensities of developed land. Two maps of the same place years apart say what changed, and how fast a county is being built over. The arithmetic is simple, counting pixels and multiplying by their area, but categorical rasters have their own rules: they cannot be averaged or resampled like temperatures, a declared nodata value can hide real zeros, and every product has conventions about which changes it records.

The guides here work through real data: NLCD for every year from 2001 to 2021, cut from MRLC’s web coverage service, and ESA WorldCover at 10 m. In Williamson County, Texas, developed land grew from 332 to 523 km² while the population more than doubled, and three Brushy Creek subwatersheds passed 25% impervious cover.

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