Not that it matters to small UAV operators, but be very careful when reading interpretations of the regs that do not quote the reg.
Above is a perfect example.
91.119 reads:
"91.119 Minimum safe altitudes: General.
Except when necessary for takeoff or landing, no
person may operate an
aircraft below the following altitudes:
(a)Anywhere. An altitude allowing, if a power unit fails, an emergency landing without undue hazard to
persons or property on the surface.
(b)Over congested areas. Over any
congested area of a city, town, or settlement,
or over any open air assembly of persons, an altitude of 1,000 feet above the highest obstacle within a horizontal radius of 2,000 feet of the aircraft.
(c)Over other than
congested areas. An altitude of 500 feet above the surface, except over open water or sparsely populated areas. In those cases, the
aircraft may not be operated closer than 500 feet to any
person, vessel, vehicle, or structure."
(And helicopters have a bit of an exemption as long as they don't pose a hazard.)
"(1) A
helicopter may be operated at less than the minimums prescribed in paragraph (b) or (c) of this section, provided each
person operating the
helicopter complies with any routes or altitudes specifically prescribed for
helicopters by the
FAA;"
Nowhere does it say that congested areas are defined on any chart, though the yellow areas on sections certainly are, but they are not in any way exclusive.
The FAA has specifically not identified what a congested area is, and rules on a case by case basis.
As an example, a beach could be, a road with a number of cars could be, and a picnic could be.