A question about scale:

for the world map it's 1km = 0,25 pixel
For regional maps, what scale should we use ?
If I make the map 10 times larger I get a file of 2700 x 2700 pixels when I take the red selected area. I admit it's a relatively large area so we could go with something bigger but we need to have a reasonable size.
with this we have 1 km = 2,5 pixel

10 times larger, does this sound OK, too small or too big ?


I was also wondering about the rivers. Does the new landscape influence the waterflow? What method do you use to decide where to put them ?