pointswithin

Pointswithin is a geospatial concept and operation used to identify points that lie inside a defined boundary, such as a polygon, multipolygon, or other area geometry. It is commonly employed to extract a subset of points, to count occurrences, or to enforce spatial constraints in analyses and data management. The exact interpretation of “within” can depend on the software or library, particularly regarding whether points on the boundary are considered inside; this should be clarified for each tool.

In practice, pointswithin appears in a variety of platforms. In PostGIS (SQL for spatial databases), the operation is typically expressed with functions like ST_Within(point, boundary) or via spatial joins, for example: SELECT p.* FROM points p JOIN boundaries b ON ST_Within(p.geom, b.geom); In GeoPandas or Shapely (Python), a point object has a within method (point.within(polygon)) or a spatial join can be used to find all points within a polygon. In R with the sf package, st_within(points, boundary) serves a similar purpose. Many GIS applications expose a “Select by Location” or “Spatial Join” tool to perform the same task without writing code.

Applications include selecting sampling sites within a study area, aggregating data by polygon, quality control, and environmental reporting. Best practices involve ensuring consistent coordinate reference systems, enabling spatial indexing for performance, and explicitly handling boundary cases to avoid ambiguity about points exactly on the boundary.

Related concepts include contains, intersects, and within, which describe different spatial relationships and can be used to tailor queries to specific analytical needs.