2

After using the Union tool on QGIS I get hundreds of gaps and overlaps between polygons on the resulting shapefile. If I zoom to the fullest on those gaps and overlaps they are always lines, they never show any area. Sometimes the error disappears after I move the vertices associated with the gaps, but it doesn't always happen and there being hundreds of errors it would take a lot of time. Is there any solution for not getting this kind of error, or any way I can fix my shapefile? .The images shows part of the shapefile where you can see the erros, wich are just lines between polygons

PolyGeo
  • 65,136
  • 29
  • 109
  • 338
Gonçalo Coimbra
  • 21
  • 3
  • 2
    You could try a small buffer before unioning – Ian Turton Nov 04 '23 at 16:41
  • Maybe a valid answer? – Babel Nov 04 '23 at 16:42
  • You can also try snap to grid before and/or after the union – BERA Nov 04 '23 at 19:55
  • Just tried snap to grid and got more errors than before. I left the 1 meter grid spacing that comes default, are there better values? Thank you – Gonçalo Coimbra Nov 04 '23 at 20:18
  • What type of layers are you using, shapefiles, file geodatabases. geopackages, etc.? If a file geodatabase does an input have true curves and what is its validated tolerance? I would check my inputs geometry and run a v.clean with a suitable tolerance followed by remove duplicates on each layer, then try the union. – John Nov 04 '23 at 22:43
  • This is a common issue because most GIS formats are not aware of topology. There are many old questions and answers about the topic. Some examples: https://gis.stackexchange.com/questions/71809/is-there-a-dissolve-st-union-function-that-will-close-gaps-between-features https://gis.stackexchange.com/questions/247205/solve-wrong-topological-error-after-union https://gis.stackexchange.com/questions/277334/shapely-polygon-union-results-in-strange-artifacts-of-tiny-non-overlapping-area. – user30184 Nov 05 '23 at 15:31

0 Answers0