OpenStreetMap
I could really use some advice on rivers. I've been trying to fix the Potomac River in Washington, DC, and failed at three attempts so far.
FWIW, I've got several different things going on in there right now to see what renders correctly next week.
natural:coastline seems to be the cheapest, but a total cop out for rivers.
The linked, proposed method descriped in the map features wiki just doesn't seem to work at all.
Discussion
Comment from daveemtb on 4 September 2008 at 16:22
The rendering of large rivers on Mapnik isn't working yet, but it should show up fine in Osmarender. Believe it or not, some are suggesting that all tidal river banks should be tagged as coastline! Please contribute your opinion at osm.wiki/index.php/Tidal_Rivers as once this is agreed, Mapnik might be updated to render large rivers properly!