Who can use this feature
Editors of a project within a Professional or Pro + workspace.
Selection requirements for tool to work
At least two overlapping polygon features
Donuts aren't just tasty, they are super important in geospatial analysis too!
Often when we digitise large areas, either manually or through the geoAI tools (e.g. magic wand, feature finder), our polygons cover areas that are not actually part of the category we are mapping.
In the animation below, you can see how one polygon covers the whole island including all the beach, while another covers the main part with the buildings and vegetation without the beach.
But what if we are interested in separating the beach?
We could digitize the beach, but are likely to have gaps and overlaps between the beach and the forest. These topological errors lead to miscalculations in area coverage. It's also quite tedious.
Instead, we use the subtract tool.
Subtracting polygon features or layers from each other allows us to 'cut holes' or 'chunks' out of one feature with another.
How to use subtract:
Make sure that the feature/layer that will be subtracted from (i.e. the donut bready bit) is higher up in the table of contents from the 'hole' to be cut out. Rearrange the layers if required.
Select the layer/s or feature/s required.
From the context menu in the top menu bar, click the arrow next to the 'dissolve' tool to access more options.
Click on the
subtracttool.You can also access subtract via the shape tools under the toolbox menu item, or by using
ctrl + alt + -shortcut).Note that if you accidentally subtract in the incorrect order, you can always undo (ctrl + z) and try again.
