Dale, all edges crash; top, bottom, left, right (actually I havent tried the right) I could understand if I was trying to place the river along the edge of the tile but I am coming into the edge of the map at a right angle. So the river I am trying to draw is in between two tiles that are on the edge row(or column) of the map. It should not be affected by the fact that the map does not warp as it has nothing to do with the (imaginary?) row of tiles just off the edge of the map. As soon as you hit an edge tile with river tool selected, crash to desktop. Does not seem right to me.