Union

The Union operation is  an especial kind of union. It computes the intersection between Input Layer (A) and  Overlay Layer (B) generating one geometry for each intersection, it computes the difference between A and B, and also computes the difference between B and A. All geometries generated by these three steps will be part of the result. 

The attributes from A and B can be selected to compose the result. The geometries generated by the intersection will have values for all attributes selected by A and B. The geometries generated by the difference between A and B  will have values only for the attributes originally from A, and the geometries generated by the difference between B and A will have values only for the attributes originally from B.

It is accessed through:

    Processing > Vector Processing > Union...

1. Input Layer (A): select the layer A  apply the union operation. 
• Only Selected objects:  optionally chech this box to apply the union only over selected objects n Map Display.
2. Overlay layer: select layer B to compute the union with. 
• Only Selected :  optionally chech this box to apply the union only over selected objects on Map Display.
3. Attributes:  choose the attributes from both Layers (by clicking over) and moving then to right side.
4. Output Object Type: default is Single objects, meaning it will generate simple geometries.  Multi Objects means the geometries can be grouped (MuliGeometry).
   
5. Output Repository:  inform the repository by clicking on:
• to select the output directory and also inform the new layer name to store the result, or
•  to select the output  Data Source (giving its connection parameters).
• Layer Name: inform the new layer name to store the result at the data source.
6. Click OK to perform the operation or Cancel to close the interface.