Primary sample unit

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A Primary sample unit or PSU is an area of land, typically square to rectangular in shape, that is approximately 40, 100, 160, or 640 acres in size. Within the PSU, sample points are assigned. Certain data elements are collected for the entire PSU, while others are collected at the PSU points. The size of the PSU is based on the shape, size, and complexity of the resources being inventoried. In 34 states, PSU’s are often 160-acre square parcels measuring 0.5 mile on each side. In the western United States, PSU’s are often 40-acre or 640-acre square areas; the 40-acre units are used in most irrigated areas, and the larger PSU’s are used in relatively homogeneous areas containing large tracts of rangeland, forest land, or barren land. In the 13 northeastern states, PSU’s are defined to be 20 seconds of latitude by 30 seconds of longitude, ranging from 97 acres in Maine to 114 acres in southern Virginia. In Louisiana and parts of northwestern Maine, PSU’s are 0.5 kilometer squares (61.8 acres).

References

List of USDA terminology

United States Department of Agriculture Terms

Aerial photograph; Artificial and modified surfaces; Barren; Barren land; Beach; Census water; Climatic factor; Close-grown crops; Conservation practice; Conservation Reserve Program; Conservation Reserve Program land; Cover and management factor; Cowardin system; Cropland; Cropping history; Deepwater habitat; Developed land; Erodibility index; Erosion (USDA); Estuarine Wetland; Farmsteads and ranch headquarters; Field; Forest land; General cover; Growing season; Habitat composition; Habitat configuration; Habitat patch; Hayland; Herbaceous; Horticultural cropland; Irrigated land; Lacustrine System; Lake (land type); Land capability classification; Land cover/use; Large streams; Large urban and built-up areas; Large water bodies; Marine System; Marshland; Mines, quarries, and pits; Minor land cover/uses; Mud flat; Open canopy short woody plants; Open canopy tall woody plants; Other aquatic habitats; Other rural land; Ownership; Palustrine Wetland; Pastureland; Perennial stream; Personal Digital Assistant ; Photographic interpretation; Practice factor; Primary sample unit; Prime farmland; Railroads; Rainfall and runoff; Rangeland; Remote sensing; Reservoir (land type); Ridge roughness; Riverine System; Riverwash; Row crops; Rural transportation land; Saline deposits; Salt flats; Sample point; Sand dunes; Sheet and rill erosion; Short woody plants; Silviculture; Slope (land type); Slope length; Slope-length factor; Slope-steepness factor ; Small built-up areas; Small streams; Small water bodies; Soil erodibility factor; Soil erodibility index; Soil loss tolerance factor ; Soil survey; Stream (land type); Tall woody plants; Universal soil loss equation; Unsheltered distance; Uplands (land type); Urban and built-up areas; Vegetative cover; Water (land type); Water areas; Water body; Water spreading; Wetlands (land type); Wetland losses; Wind erodibility group; Wind erosion; Wind erosion equation;

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