Which should be considered 'front door

[myfs_100929]

Thank you for such an informative site! I'm trying to map out my home to identify the different sectors but I'm stuck as to which I should consider my front door. I live in a three family home (each apartment has it's own floor and we're on the street level floor). The door that goes out to the front (street side) of our house is used very infrequently- by the occasional visitor and by us only to check the mailbox. The back door is used by our family to enter and exit the house (our garage is back there) and by our closest relatives when they come to visit. I'm thinking that our back door should be our "front door" when placing the nine squares over a plan of our home but I would appreciate your expert advice. Thanks for your help.
Sincerely,
Stacey Ranchy