[GIMP] Smooth path line?

[TNTeener]

Hello. On my map i want to add something like a trade route. like here:
Late_Medieval_Trade_Routes.jpg
But when i try to make a path and draw along it it doesn't look very smooth? Any trick to make it better? Plug-in, script?

[Freodin]

Can you be a little more precise in identifying your problem?

Is the curve not smooth enough? Or does it look blocky? Is the anti-aliasing not good enough?