This tool splits vector layers at their overlaps, creating a layer containing all the portions from both input and overlay layers. The Union is related to the Boolean OR operation in set theory and is one of the common vector overlay operations in GIS. The user must specify the names of the input and overlay vector files as well as the output vector file name. The tool operates on vector points, lines, or polygon, but both the input and overlay files must contain the same VectorGeometryType.

The attributes of the two input vectors will be merged in the output attribute table. Fields that are duplicated between the inputs will share a single attribute in the output. Fields that only exist in one of the two inputs will be populated by `null` in the output table. Multipoint VectorGeometryTypes however will simply contain a single output feature identifier (`FID`) attribute. Also, note that depending on the VectorGeometryType (polylines and polygons), `Measure` and `Z` ShapeDimension data will not be transferred to the output geometries. If the input attribute table contains fields that measure the geometric properties of their associated features (e.g. length or area), these fields will not be updated to reflect changes in geometry shape and size resulting from the overlay operation.

## See Also

intersect, difference, symmetrical_difference, clip, erase

## Function Signature

`def union(self, input: Vector, overlay: Vector, snap_tolerance: float = 2.220446049250313e-16) -> Vector: ...`

## Project Links

WbW Homepage User Manual Support WbW