[GIS] How to make dashed lines between adjacent polygons render correctly in QGIS

Question

I have adjacent polygons that I want to be marked out with dashed or dotted lines. This sometimes works but there appears to be a problem where the pattern isn't always synchronised on the shared boundaries which leads to odd patterns or solid lines. Is there a simple way round this?

Using GQIS 2.10.1 Pisa

Answer 1

To this kind of interesting but recurring cartographic question, there is different approaches (some suggested in the comments):

• The classic approachs is to use dashed lines with a white solid line below to hide the overlapping lines. The downside is that it's not effective if you have a colored background or multiple representations.
• The other approach is to convert your polygons to polylines, remove overlapping line either by merging them together or using clean tools like MMQGIS / Delete Duplicate Geometries or v.clean in GRASS. Then you will have only one line to map and no more problems with dashes.
• My favorite is to offset lines towards the inside of each polygon, therefore avoiding any overlap while keeping the line symbology of each polygon, especially in case of different dashes, symbology and colors you would like to keep visible in thematic mapping.