submarket population size criteria: large multifamily properties

[Hassan O.]

Is there a rule of thumb that any of you follow in regards to submarket population size in a zip code or census tract for different sizes of multifamily properties? For instance if an MSA has a population of 4M people, then for a 50 unit complex what are your minimal submarket population size criteria in a Specific zipcode, census tract or geographic radius, versus that of a 70 or 100 unit property? x number of units per xx of population...

It's relatively easy to get zip code population data, many of which can be very large and may have up to 15,000 people, another 30,000, 50,000+ etc. What do you use to dissect even further?

I have my personal criteria, seeking other points of view

Thanks