distributor mapping is measuring and plotting the timing advance curve. to do it accurately u need a dyno but a rough indication can be done free-revving in nuetral.
it's done by drawing a graph with RPM on the horizontal axis and timing degrees on the vertical axis. starting at idle, and using an adjustable timing light, increase the rpm at intervals of 100 rpm and plot on the graph what the actual igniton timing is. the pattern should look very similar to a torque curve. this is only a rough guesstimation if not done on a dyno because the vacuam advance wont be in full operation without any load.
the easiest way to "remap" this is to remove the breaker plate inside the distributor and change the springs for the centrifugal weights. stronger springs = less advance, weaker springs - higher advance. i have never had to regraph a ford distributor(they got it right the first time) but on the commodore red and blue motors you could get noticable power increases by fitting v8 springs into the 6cyl distributors - and it fixed the "unfixable" pinging they had.
the reason for remapping/regraphing a distributor is to align the igntion timing advance with the "power band" of the cam thus raising the torque curve.
