you ever hear of a family tree - your mom your pop your sisters your brothers grand parents great grandparents.....

system map is making a family tree of your alters..

mine has these things on it (keep in mind I was in treatment for years and this represents years of working on my DID and my final destination was where I am now living as an integrated person) -

whos is charge
the protectors
the helpers
the treasurer or banker
the cook
the baby sitter
the maid
the ones that worked outside the home and what their jobs were

alters names
their ages
jobs
type or personality (happy sad creative angry curious shy outgoing)
things they liked
things they hated

how the separating happened (who sprang from who is another way to put it)

what their symptoms if dissociating were
what their triggers were

there was more on mine than whats here but this will get you started thinking on how your system is comprised.