Difference
The 'Difference'
The “Difference” geoprocess works with two layers, the “input layer” and the “overlay layer”. It is known as “Spatial NOT” and allows you to obtain the areas in a layer which are not present in the other layer. The geometries in both the “input layer” and the “overlay layer" must be polygons, lines or points. The alphanumerical schema of the “input layer” will remain intact in the "result layer", as in the end it gives more information about it.
This geoprocess is very useful in numerous situations. For example, it can be used to complement the "Clip" geoprocess. If “Clip” allows you to exclude everything that does not belong to a geographical area under study, "Difference" allows you to do exactly the opposite; exclude a specific area from our working layer.
A useful example:
Transferring territorial jurisdiction between different governing bodies. Thus, if the national government transfers certain jurisdiction to a regional authority, it can decide to exclude the geographical area of the transfer in question from its data bases.
Running the 'Difference' geoprocess
Running the “Difference” geoprocessClick on the “Open Geoprocess” button to access the dialogue window which allows you to run the "Difference" geoprocess.
You can enable the “selected features” check boxes at this point of the geoprocess for the input layer and the overlay layer. If you click on the “Ok” button, the geoprocess will be run.
In the following image, the “Difference” geometry appears in black between a flood zone and one of the selected cities or towns. In this case, the new layer resulting from the calculation of the difference will take the schema (alphanumerical attributes) of the geoprocess input layer.
