What does it mean to "narrow down postal codes"

[applicant15]

I'm trying to find household data by looking at census tracts, but my prof said there is too many postal codes and need to narrow those down. How do I know which postal code is important or not? Do I just group postal codes that are in one area as category A, then another group as category B, and so on to differentiate the regions? Will also be using SPSS.

[rising_star]

This is impossible to answer without more information. Why not just ask your professor what they meant?