I’ve got a shapefile of Switzerland. Shown Polygons are 6-digit ZipCodes. Whenever I dissolve the file for example by 4-digit ZipCodes, it results in incorrect polygons.
Unfortunately some polygons borders aren't touching. If I zoom in on the orignal shapefile, it seems like there are empty spaces between the polygons.
I'm using QGIS and R and I've tried a lot. This is my first time using GIS data.

