Looking at the clip from your map just a couple of comments.
Are you using coastline layer in 'burn' mode to make what is a faint PS brush darker? It does leave it a bit pixellated. Instead of burn, you could try one of the edge detect filters on the complete layer (in normal mode) Obviously, keep a backup just-in-case. screenshot https://i.imgur.com/vCvXkIE.jpg Might be an improvement.
I can see a join in the background. No good trying to blur your way out. Make a new parchment pattern that is tile-able.
The plugin for this is resynthesizer. You can get a Windows version here. https://www.gimp-forum.net/Thread-Resynt...or-Windows Windows version is old but still works.
Make a new pattern from the old. Export as a png to your patterns folder. Comparison. https://i.imgur.com/v535uzQ.jpg
Are you using coastline layer in 'burn' mode to make what is a faint PS brush darker? It does leave it a bit pixellated. Instead of burn, you could try one of the edge detect filters on the complete layer (in normal mode) Obviously, keep a backup just-in-case. screenshot https://i.imgur.com/vCvXkIE.jpg Might be an improvement.
I can see a join in the background. No good trying to blur your way out. Make a new parchment pattern that is tile-able.
The plugin for this is resynthesizer. You can get a Windows version here. https://www.gimp-forum.net/Thread-Resynt...or-Windows Windows version is old but still works.
Make a new pattern from the old. Export as a png to your patterns folder. Comparison. https://i.imgur.com/v535uzQ.jpg