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I have a map originally as a shapefile. The map includes a country (mainland) and an island far away from the mainland. I want to cut the map so that only the mainland is shown and save it again as a new shapefile. The problem is that the island is tied in the same polygon as one of the mainland regions.

How would you advise me to split the map?

I am using QGIS 3.10.5.

she_weeds
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Luis Pinedo
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3 Answers3

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Start editing the shapefile. There is an Explode tool available while editing that will convert a multi-part feature into individual features. In ArcMap, from the Editor toolbar select Editor > More Editing Tools > Advanced Editing. A multi-part feature must be selected before the tool will become active.

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Bjorn
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  • Not OP, but could you include a screenshot to show what you mean by the explode tool? I don't see it in the advanced digitising toolbar, only Split Parts (which requires you to draw a line through), although there is such a tool with the plugin Digitizing Tools. – she_weeds May 04 '20 at 02:32
  • Note: When I originally posted this answer the question did not have the QGIS tag. – Bjorn May 04 '20 at 12:32
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    The answer is the ArcGIS solution while editing. QGIS would use the split parts tool in an edit session. Both programs have multipart to singlepart tools that will split all the parts in a layer. – John May 04 '20 at 12:32
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You can use the multipart to single parts processing tool which has been around since nearly the beginning of QGIS this will create a new layer of single parts

To avoid having to create a new layer you can use Edit In-Place mode for the above tool in Processing Toolbox.

With both you can select only the features you want split before running the tool.

Alternatively you could use the Advanced Digitising Tools plugin and split features in the interactive mode which will let you click on a feature to instantly split it (or click on just a single part to split that off).

Once you have split off a part you can then select it and save that as a separate shapefile

she_weeds
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Just to add to the other answer (ie. convert from multipart to singlepart) be avare that the attribute may become inaccurate/wrong/non relevant after converting as each part of the polygon will inherit the attribute of the original multipart polygon (so if you have a population field for exemple you will still get the population of the whole country (island+mainland) for the island part even if the population is only a fraction of that)

J.R
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