after using the vectorizing tool I get the following result (picture). Around the cells you can see a small "boundary". This thin line is transparent and annoying. Is it possible to remove these small transparent areas?
simmilar problem here ...
and i've tried all the suggestions form above and found some other sources, like http://gisforthought.com/polygon-outlines-in-qgis/ and How to remove tiny polygon outlines in geoserver sld? ... without beeing successful.
so i finally set up a test-polygon-file with a regular structure based on non-overlapping and gap-less squares (see pic. 1 - with identical point coordinates at the corners). displaying these polyogns with white "Simple Fill", outline style: "No Pen", units: "Map Unit" on top of a magenta project-background shows that "small tansparent outline effect" (see pic. 2) . these "gaps" are
- not a result of the underlaying polygon-data (non-overlapping and gap-less!)
- scale-independent ... they vary in size but do not vanish completely in any scale
- are displayed in qgis as well as in print composer outputs (showing differnt dimensions in bothe of them!)
- and removing these "lines" by setting corresponding border color manually is just a workaround, which isn't really comfortable in particular if you use a lot of graduated symbols layers.
so, acctually i can't provide answers but give some inputs for narrowing down the problem ... but in 2013 that was discussed in the context of "the gamma parameter of the Java antialiasing" - see andrea aime's comment How to remove tiny polygon outlines in geoserver sld?