Here is a typical concert harp:
The soundboard rises in a straight line from the lower notes to the higher ones. This makes sense as you would expect shorter strings for the higher notes. However, the shape of the neck is more complex. If length were the only factor determining the pitch (I know that it isn't) then the shape would be wrong. The strings would need to decrease in length geometrically. Is there a good physical reason for this shape or is it determined by tradition and aesthetics?
One feature that makes some sense is that the top few notes cease to get (much) shorter. I guess that this is for the obvious reason that if they got too short then they could not be plucked.