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Sorry for the confusing question. I have a shapefile and I need to draw a polygon in the middle of it. I know I can use the "create features" function, but that creates a polygon on top of the first one, whereas I need it to cut into the main polygon and reduce the area of it, rather than being an independent feature sharing the same space. The same way that the "cut polygons" function divides up the original polygon, but I can't always start from an edge.

Does that make sense? It seems like such a simple procedure but I can't find any way to do it.

I've attached an image to help explain. When I select the main polygon, it doesn't highlight the edges of the smaller polygons within it, meaning they're not altering the shape/area of it.

enter image description here

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  • Have you tried 'donut polygon'? If you already have the smaller polygons, try a 'erase' tool.
    – blu_sr
    Commented Jul 2, 2017 at 11:04
  • Thanks for your reply. Unfortunately 'donut polygon' still creates polygons on top of the larger ones, and 'erase' seems to only work when the smaller polygons are part of a different shapefile.
    – Stovasaurus
    Commented Jul 2, 2017 at 11:40
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    There is already a sub-tool called Clip where you can decide what happens to the parts intersecting, either discard or maintain!
    – fatih_dur
    Commented Jul 2, 2017 at 14:17
  • @fatih_dur That might be worth expanding into an answer
    – Midavalo ♦
    Commented Jul 2, 2017 at 22:01
  • Thanks for the info fatih_dur, but the Clip feature only works on the intersection between two different shapefiles rather than different polygons within the same shapefile.
    – Stovasaurus
    Commented Jul 3, 2017 at 5:47

2 Answers 2

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There are several ways to achieve this.

  1. try topology tools to fix overlapping polygons. Create a 'topology', use 'must not operlap' rule, and then 'error inspector' window to fix them
  2. give the cut polygon another chance. Use the 'trace' tool to digitize the small polygons out of the large ones. This is same as 'donut-tricks'.
  3. sometime converting shapefile to coverage and back into shapefile fixes overlapping issues
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  • Thanks heaps for your help. To be honest I couldn't get 1 and 3 working (I think topology works differently on 10.2), but the cut polygon tool does seem to work under the right circumstances, so thanks for that!
    – Stovasaurus
    Commented Jul 3, 2017 at 7:55
  • Thanks for accepting, but I prefer #1 to be a more elegant way (so I put that in 1). You need to create a geodatabase, put your file in it and do the rest (there are a many tutorials online like this). This tool repairs errors even if they cannot be seen in full extent. #2 on the other hand is a sloppy process and creates 'sliver polygons'. You can call #3 as a 'backdoor hack', taking privilege of the coverage file system who doesn't support 'multi-polygon' feature.
    – blu_sr
    Commented Jul 3, 2017 at 8:25
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As an alternative to the accepted answer, there is already a command called Clip in the Editing Toolbar where you can decide what happens to the parts intersecting, either discard or maintain. It works for not only one but more than one layer that are editable. Just a word of advice, editing in ArcMap can be a little bit tricky in terms of what is selected on which layer. As long as you make one layer selectable, your life will be much easier as editing.

Moreover, if you have many features intersecting on one layer/feature class where you want to discard the parts intersecting, you can use a workflow that I prefer: (1) Self union, (2) Spatial Join with ARE_IDENTICAL_TO operator, (3) Dissolve on a unique value field inherited from the first union. This was also given and answer to another question, https://gis.stackexchange.com/a/219606/28687

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