A mapped instrument is used just like a standard instrument, but each individual input note can be:
Named (snare, hi-hat, and so on)
Mapped to an output note
Given a velocity offset
Assigned its own MIDI channel
Sent to one of up to 16 output cables (This allows you to create a single instrument that addresses multiple sound sources.)
Given its own notation parameters: note head shape, relative vertical position in the staff, and drum group assignment (See Use mapped staff styles for drum notation in Logic Pro.)