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I have a vector file where I have made some polygons but between the polygons I have empty space.

This entire empty space I would like to make one whole polygon but until now I can't figure out the way to do it.

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The easiest way to do this is to create a polygon that covers the extent of your area of interest and turn on "avoid intersections" when drawing it.

So initially I have some polygons: enter image description here

I then turn on snapping: go to Settings > Snapping Options... and for Layer selection dropdown choose Advanced.

You must have this set up correctly. I usually recommend a tolerance of 20 pixels, and make sure to tick on "Avoid intersections".

enter image description here

Then you can simply draw a polygon that covers the area you want filled:

enter image description here

Because the new polygon cannot intersect existing ones (you turned on avoid intersections), you get one that fills in just the gaps:

enter image description here

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    @elena If the answer is correct you can accept it by clicking on the green check mark next to the answer. This helps keep track of answered and unanswered questions. – HeikkiVesanto Jan 11 '17 at 9:29
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You can do this using the following steps:

1- In QGIS go to Vector > Research Tools > Polygon From Layer Extent, and use the existing polygon layer as Input File. Choose the Desired name for the output file name of extent layer. This will create a new polygon layer covering all polygons.

2- Use Geoprocessing Tools > Difference: Use the extent layer created in step one as input file and the existing polygon layer as difference file. Then You will get an opposite shapefile which covers the empty space.

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Make a new polygon layer and add a polygon with the border of your area of interest. Make a union of your two polygon layers. For example: You start with these polygons your original polygons

Create the outer border polygon as a separate layer enter image description here

Make the union of the two layers from the menu Vector/Geoprocessing Tools/Union enter image description here

In the result layer above we have four polygons.

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  • Not Union. This makes one polygon with all the shapes of both features, he want's just the empty space. That's under Vector -> Geoprocessing Tools -> Difference. Then you want to select border, and small. – Evan Carroll Jan 10 '17 at 21:12
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    @evan It is false you will get several polygons after union. Did you try it? – Zoltan Jan 11 '17 at 8:29
  • @evan after difference you will get one polygon with all the areas outside the small ones. With union you will get the outside and inside polygons in one layer. – Zoltan Jan 11 '17 at 9:50

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