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I have a shapefile which contains many polygons and because I work on a large geographical extent, I'd like the polygons to be slightly bigger, for presentation purposes. Basically keep their extent and enlarge them by, say, 30% for example. I was thinking of using the SAGA "transform vector layer" tool. However I get lost when I need to put the X and Y coordinates, as shown in the picture below:

enter image description here

I understand that the scale factor will enlarge the polygons by whatever factor I want, but when it comes to the X and Y I wonder what I should put. I can't seem to find the x and y coordinates of my shapefile. I read this post Enlarge a Polygon without changing its shape or position but it gives details for doing so for just on polygon.

Tim56
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    Can you not just increase the size of the boundary with symbology? You could also use the geometry generator to buffer the polygons. – HeikkiVesanto Feb 19 '20 at 17:17
  • @HeikkiVesanto thanks for your input, however could you develop a bit on your point please? Not sure to understand a 100% – Tim56 Feb 19 '20 at 17:19
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    If it is for presentation purposes only, why not work with the ability to style the layer instead of trying to modify the data? – Gabriel Feb 19 '20 at 17:22
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    I'm puzzled... If you enlarge them by some amount (I'm thinking buffer) then, by default, their extent must correspondingly increase. Yet you want to "... keep their extent ...). Maybe you could edit your post and include a drawing of what you have in mind. – Stu Smith Feb 19 '20 at 18:34
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    I think you can union all the polygons and use the centroid of the result for the x and y. That is the reference point from which everything is scaled. Otherwise you would need to do it in a loop. Why not just buffer the polygons using mitre joins to keep the corners sharp? – jbalk Feb 19 '20 at 19:51
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    @HeikkiVesanto Yep, that's all I used to do. Just increase the symbol's border thickness (and not have it black - usually use the same colour as the polygon itself). – user25730 Feb 19 '20 at 23:16
  • @StuSmith, I used the wrong term sorry. What I meant by extent was that I didn't want the centroid of each polygon to move. – Tim56 Feb 20 '20 at 09:24

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The simplest approach would be to increase the size of the polygon outline in the appearance of the layer, or buffer the polygons by an amount that would give the look you're going for. You could put the buffer on the map for the images, but provide the original data for the people who actually need to work with it.

Mon Mo
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  • I've followed your approach, I've saved my shapefile and gave it a new name, and worked on that new layer without modifying the previous one. I put a buffer of 100m around each polygon, and it comes out more explicitly in the map, thanks. – Tim56 Feb 20 '20 at 09:21