Zonal Statistics
Definition
Zonal statistics compute summary values of a raster (or point measurements) within specified polygons—mean rainfall per county, maximum temperature per park, sum of population within flood zones. Options include variance, standard deviation, quantiles, and histograms. Accurate results depend on sampling strategy, nodata handling, and alignment of raster and vector grids.
Application
Policy dashboards, environmental compliance, insurance risk scoring, and academic studies all rely on zonal statistics to translate raw surfaces into comparable indicators.
FAQ
How should nodata be handled?
Explicitly exclude nodata and report coverage; if coverage is low, flag results as unreliable or fill with modeled estimates.
When do histograms add value beyond means?
They reveal multimodality and extremes—useful for planning where tails drive risk (e.g., heat exposure).
What sampling method is best at mismatched resolutions?
Area-weighted sampling or rasterization of zones at the source resolution avoids bias from point sampling of cell centers.
How to make results reproducible?
Record software, parameters, data versions, and CRSs; store scripts alongside outputs.
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