My fantasy world is very crowded. It has a late medieval renaissance feel. Gunpowder ect. as such there all lots of nations of varying sizes covering all 3 land masses (not the whole globe). For a while it was getting confusing for me to tell the difference between coast, river and border.

For the coast I have the normal line but in capes and bumps on the coast I put a second line around it.

For rivers i just have a continuous smooth flowing line.

and for borders I have a small thin dashes with a dot between each dash.