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This is more of a cartographic style question, using QGIS.

I have a dataset that consists of land parcels (previous archaeological projects) as polygons. Multiple projects from different years share the exact same spatial shape.

In composer, I would like to export a map that somehow can show that there are multiple polygons on top of each other, and also include all of the labels.

Currently, I am unable to show more than one shape except by manually decreasing the offset for the top polygon and making it slightly smaller than the one it is on top of.

Is there a better way to do this or to automate this process in the dataset? I think perhaps by writing a script to identify similar parcels, and then add an offset value, so that the map would look like nested differently-colored shapes, but this seems like an awkward work-around.

  • You should use symbology. You can make some of the polygons hollow, some with hatching, some with a fill... – jbalk Nov 21 '16 at 23:54
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    If you can set transparency at color level; with expression such as color_rgba(50, 60, 70, $id * 10), could it help? I am assuming your parcels at the same place are well separated each other on the attribute table (row-wise), so that setting $id gives different transparency. – Kazuhito Nov 22 '16 at 17:57
  • Thanks, but is there a way to automate the symbology to create a unique polygon color/transparency/hatching for each feature? – kilolima Dec 18 '16 at 5:57
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If you want to style overlapping polygons (that are identical) you can try to construct them in a contour fashion. Otherwise you can do as suggested above and try different styles (opacity, hatching, point pattern fill etc.) that when overlapped give a pleasant and readable effect. The preferable option of those two, as well as the specific styles, are largely dependent on the data. Maybe if you link them i could suggest something more but from what i gather, i think the second option is the way to go. As far as the labels go it should be quite straightforward using the rule-based labeling option.

  • Thanks. The ideal is to display overlapping polygons but not have to manually specify the hatching patterns. Is there some way to pass a hatching value or seed to QGIS and let it auto-generate unique hatching patterns? – kilolima Dec 18 '16 at 5:55

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