In an ideal world you would dyno test and map an engine before it is fitted in any vehicle then once fitted the map adjusted by driving.
Mapping on the road is very dangerous and difficult as with most modified cars will probably be capable of twice the maximum speed limit in only a few seconds.
The only way to do 'road' mapping safely is to rent somewhere like Bruntingthorpe or North Weald where full throttle high speed mapping can be done, even then the car must be checked to ensure it is safe to be driven at high speed.
The down side to this is the cost which can run to thousands not hundreds

Steve