I would like to give brief overview of mapping load & incremental load below:-
Basically mapping load is used to map any code to some description. Mapping load works on key & value pair. For example if you have definition of some code in you master table. In transaction table you just have code only, so to get the description from master table to transaction table either we can use join or the better way is to use mapping load.
//Call it in transaction table
ApplyMap('MapDesc', <KeyField>, <Default value for non matching codes, it's optional>)
Incremental load is for loading incremental data. For more explantion on it please see attached powerpoint file.