Union
An operation that merges overlapping or adjacent polygons into one combined geometry.
Category: Operations · Also known as: Combine, Merge
Definition (expanded)
Union (often called Combine or Merge) returns the area covered by either input geometry. In Turf and PostGIS it's commonly union(A,B). Invalid inputs (self-intersections, duplicates) are a common reason unions fail.
Related terms
DissolveMerges adjacent or overlapping parts to remove internal borders, often producing a cleaner outline.DifferenceAn operation that subtracts one geometry from another (A minus B).IntersectionAn operation that returns only the overlap area of two geometries.Valid geometryA geometry that follows topological rules (closed rings, no self-intersections, properly nested holes, etc.).Make validA repair step that converts invalid polygons into valid geometry, often by splitting or reshaping boundaries.