Just had a reviewer question my suburban rating stating it was rural due solely to population of 42 people per square mile. In Northern Michigan, I've always considered it rural when the only people I pass on the road are Dorothy and Toto. If I look the mile stretch or so between roads and see only the subject mailbox, it's rural. If the road requires 4-wheel drive or a tracked vehicle, it's rural. If it's a 20 acre or greater parcel, it's probably rural. If the directions say you drive 5-10 miles to the next driveway and turn in, it's rural. If you see more wildlife than houses, it's rural.
No set rules, just some guidelines.
I figure if Comps are within 10 miles and within the same school district and the owners commute to nearby towns for employment, shopping, and services, it's suburban. :usa: