Reduce the spell level of magic mapping, but also reduce its utility: instead of mapping the entire level at once, you choose a point to center your divination on and a circular or square area, with a radius dependent on your divination skill, gets mapped. After this change, it might be similar enough to clairvoyance to be merged with that spell (the difference with clairvoyance is that it currently always centers on the player; perhaps the new merged spell could instead scale with skill by having a fixed mapping area, but the distance you can target it at increases with skill level.)

This does not change the scroll of magic mapping behavior, which still maps the whole level.

The spell of clairvoyance grants a few hundred turns of intrinsic clairvoyance when cast at Skilled. This makes it useful for Samurai in particular.