advance/retard ignition curves- help i don't undertsand

[piquet]

guys

ok i'm trying to get my head round ignition timing, sorry if this all sounds stupid, i get the idea, spark starts the combustion before the cylinder hits tdc, so that th fame front travels downwards so that in the time it takes to get to the piston the piston is on it's way down

now have i got this the right way round, as the revs increase you have to advance the ignition, ie the sparks is triggered earlier, because the falme front moves at roughly the same speed, but has to leave earlier to get to the piston at the same time because the piston is moving faster

now the igniton i believe is also advanced the more the throttle is open and i can't undertand why and the advance is less and less at high revs os the throttle is open more so that the advance at high revs
full throttle is less then the advance at high revs low throttle

i also always imagined that the curves would be smooth, but they often seem spikey with random troughs and lumps, why is this

sorry if this is all stupid, i'm just trying to get my head around it

pk