Organic Map Borders

Going one direction only to run into a suddenly there wall of squares can take me out of it a bit, especially when as you're approaching it looks like there is more to the area. I think 'organic' map borders would be of benefit to how the game look.
For example impassible mountains, ocean, cliffs, etc (of course with the actual current borders around them so people can't squeeze past those borders by climbing or something!)