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I'm studying for PPL and am struggling to imagine a clear "sight picture" for urban vs rural areas with regards to minimum AGL. I found that urban areas are outlined over at the Federal Census Register and are well defined, including

  • It is urban if it contains at least 4,000 housing units or has a population of at least 10,000An area will qualify as urban if it contains at least 2,000 housing units or has a population of at least 5,000.
  • Maximum hop distance 0.5 miles, maximum jump distance 1.5 miles, and no hops after jumps. Intervening, low density blocks are not included in the urban area.

Does this basically mean urban is any small town? I.e. not farm, lake, national park, etc?

As a fun side-story: when I was a kid, my grandpa worked with a cropduster that used to "dust" us kids with candy if he saw us playing outside. He was for-sure near minimum AGL.

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  • $\begingroup$ From high up it's probably easier just to look for farmland and tall buildings (4 floors or more). $\endgroup$ Jul 31, 2023 at 11:14
  • $\begingroup$ I'm struggling to understand the actual question here. Are you asking how to tell a town from a city, or rural areas? Or are you asking what the definition of an urban area is? $\endgroup$
    – GdD
    Jul 31, 2023 at 12:39
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    $\begingroup$ As you probably know, 91.119 refers to them as “congested areas” and “other than congested areas”. Interesting discussion, but zoning such as urban, suburban, rural etc. is academic when it comes to the actual regulation, and it’s really a judgement call to distinguish them while airborne. $\endgroup$ Jul 31, 2023 at 14:25

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The regulations make no reference to "urban" and "rural." It makes reference to "congested," "other than congested," and "sparsely populated." They intentionally do not define these terms anywhere. Per the Anderson interpretation, the FAA determines what "congested" means on a case-by-case basis.

The example listed is that a subdivision .5 miles by .66 miles containing 20 houses counts as "congested." At 60 houses per square mile, that's more than 10 acres per house! That population density is much less than the 500 people per square mile that qualifies an area as rural. And yet, somehow, the FAA and NTSB think this is "congested."

Here is such a congested area, a subdivision near Harwood, ND:

"congested" area

This is actually slightly denser than the hypothetical subdivision described by the NTSB as "congested."

In short, if you have to ask, you should assume the FAA will consider an area to be congested if you give them any reason to be asking about your flight. It's probably best to just treat "sparsely populated" as meaning unpopulated.

Side note: cropdusters operate under part 137. 14 CFR § 137.49 and 137.51 gives them wide latitude to ignore the part 91 minimum altitudes when it is necessary for their operations.

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