Break away from the downward pull of gravity.

(a) the gravity of the harmoutweighs the utility of the conduct or(b) the harm caused is serious and the cost tocompensate for it makes the conduct not feasible).

According to the Wikipedia definition:   "The Scaffold Law is a New York State law that holds employers and property owners fully liable when an employee becomes injured due to a gravity-related fall..."

Naturally, mid-sized more affordable, still charming cities like Richmond show up on our list for that reason.Our extended family also seems to be migrating southward, so there is the gravity that comes with that. 

That's like breaking the laws of gravity!!!...

But if it's a true septic system with a leach field, gravity takes care of it for you at no cost!

Heating systems might be gravity based (not forced air or no circulator if a boiler).

They are a simple gravity system and not that expensive in the whole scheme of things investing.

I like the list you got from @J Scott (and follow up by @Will Barnard ).Adding to JScott's very good advice about getting a copy of any perc test results (if the property is NOT on public water and sewer) is to take notice of whether the lot is perc'd for a conventional, gravity system or an alternative septic system.I don't know about Maryland, but here in Virginia many counties are strongly discouraging alternative systems by adding costs, red tape, regulations etc. when using them.

There are backwater valve for gravity systems fairly inexpensive from the hardware store, however, it can get expensive.