Union

The Union is an essential vector overlay GIS technique that integrates several polygon data layers into one dataset while retaining geometries and attributes of each original layer. The Union operation is a more complicated procedure than spatial join because it involves dividing overlapping and non-overlapping areas into several polygon features to facilitate spatial analysis of the relationship between datasets.

The Union operation is widely used in GIS, spatial analysis, cartography, land use mapping, environmental analysis, and urban planning. It allows combining land use boundaries with the boundaries of administrative regions to understand the distribution of particular land uses within these administrative units. Also, Union may be applied for comparing zoning areas, ecological zones, boundaries of properties, etc.

In the Union procedure, polygon boundaries of both input layers are retained, and the output dataset includes attributes of the participating layers. The Union operation can be performed in ArcGIS Pro, QGIS, and other GIS applications. Through integrating spatial boundaries and associated attributes, Union allows conducting overlay analysis and building geospatial datasets.