So... can you import an image into the background of Inkscape so you can be sure you're placing rivers right?

Say... flatten a current copy of your working map and export it at (presumably at full size), then import into the background of Inkscape, get your river paths just right, then zap the background.

Then somehow, going back to, say, GIMP, import the river path right into GIMP?

I don't suppose you could detail the process you use?