Impervious Surface

Fraction (0-1) or percent (0-100) of a pixel covered by impervious artificial surfaces — roofs, asphalt, concrete, compacted material — through which water cannot infiltrate. Distinct from `built-up-area`: sparse rural settlement may register as built-up while remaining only partially impervious; conversely, a paved parking lot outside any built footprint is impervious without being "built-up" in the urban sense. Flagship products: NLCD Impervious (USGS / MRLC, CONUS, 30 m, Collection 2 annual), GAIA (Tsinghua, global annual 1985-2018, 30 m), HISDAC-US (Harvard Dataverse, US historical built-up surface back to 1810), and GISA (Wuhan University, global impervious surface area 1972-2019). Consumed by hydrology ops (stormwater runoff, SCS curve number), urban heat-island analyses, and CSRD / EUDR-adjacent impact assessments.