[OSM-talk] OTG rule, borders & mountains existing | Re: Crimea situation - on the ground

[stevea]

On Feb 11, 2020, at 3:45 PM, Mateusz Konieczny via talk <talk at openstreetmap.org> wrote:
> OTG is not "everything must be mapped on survey", it means
> that direct survey (what is actually existing) overrides official data, opinions and desires.

I thank Mateusz for making (reiterating?) this important point.  I believe some of us think OTG is an absolute rule which states "map what is on the ground."  Logically, we should be able to "derive" the potentially equivalent statement "if you canNOT see it on-the-ground, you may NOT (should not) map it."  But that's not how we map, due to numerous counter-examples (some boundaries, mountain ranges, oceans...).  So, a crucial way we DO map is "if it IS on-the-ground, then THAT is what we map."  The idea of "if OTG, map THAT" shouldn't be different, but is different from "if not OTG, you may NOT map this" (which isn't true, strictly speaking, due to counterexamples).  I think in logical terms this might be called "a fallacy of the contrapositive."  Logically, this is problematic.

Start with "If A, then B" where A is "it is on the ground" and B is "you may map it."  Now, try the contrapositive "If not B, then not A" (in logic notation:  ¬B -> ¬A).  Or, "You may not map it if it is not on the ground." Usually, "proof by contrapositive" works, as "a statement and its contrapositive are logically equivalent, in the sense that if the statement is true, then its contrapositive is true and vice versa."  But in OSM, this does NOT work, because of the preponderance of examples where ¬B -> ¬A fails:  in some cases we DO map it, even though it is not on the ground.  And therein lies what we have to fix:  proof by contrapositive fails, when it shouldn't (logically), because OSM has made and does make numerous exceptions.  Let's clarify how, when and why we do this, at least as a "first cut" at how we address this contradiction.

I hope that clarifies, it does help sharpen focus about OTG in my mind, simply by being stated clearly.  Well, stated logically — and for some, I realize, that might NOT be clear!

SteveA