not as simple as that, not everything is linear,you must of heard of igntion "curve" ,for example in theory if you boost an engine by 1 bar then you will need twice as much fuel and igntion but this is not the case,as you put extra charge in, the compressed air whether it be turbo or supercharged the air is heated from compression therefore there is actually less oxygen in the air charge,i would start at idle and then go every 1000rpm,alot is guess work but on a rolling road you actually see the effects the changes you are making can have on power and torque.
another non linear factor to engines is the v.e or volumetric efficency,the restrictions in the intake and exhaust of engines can effect the amount of charge that is in the cylinder,you could have 1 bar boost and at 3000rpm the cylinder will have a high effeciency, as the piston moves faster the speed of the air flow gets restricted by the size of valves etc and the actual charge in the cylinder gets less,this is reflected in many torque curves for engines and has to be taken into consideration when mapping an engine,I think alot of it is trial,you can hold a car on a set rpm and load and add fuel and igntion and see the torque rise but at a point it will go start to decrease.You can do this every 1000rpm to start and then interpolate between them all and this will give a ball park figure map.I am no expert and alot of the guys out there map cars everyday and i'm sure they each have there own way of doing it.