withinregion

withinregion is a concept used in geographic information systems and data analysis to describe the practice of restricting analysis to data points, features, or measurements that lie within a defined geographic boundary. The region is typically specified as a polygon, though other boundary types such as multipolygons or bounding boxes may be used. The core operation, often described as a containment test, determines whether a given feature is inside the region or whether two geometries intersect to produce an interest area.

In practice, analyses that employ withinregion first establish a consistent coordinate reference system, then apply a spatial predicate such as point-in-polygon or polygon containment. The region may be an administrative boundary, a natural feature, or a user-drawn area. This approach enables localized statistics, modeling, or filtering, yielding results that reflect conditions within the target area rather than the entire dataset.

Common use cases include calculating metrics like mean income, crime rates, or precipitation within a city or watershed; performing environmental impact assessments restricted to a protected area; or clipping datasets to a region of interest for visualization or reporting.

Implementation often occurs within GIS and spatial databases. Examples include SQL queries using spatial predicates (for example ST_Within or ST_Contains in PostGIS), spatial joins and clipping operations in GIS software, or geometry libraries in programming languages (such as Shapely in Python). Edge cases include points lying on the boundary and inaccuracies in boundary data or projections that affect containment.

See also: point-in-polygon, spatial join, geometry overlay, region of interest.