[splonk]

OSL is also the IATA metropolitan city code for Oslo, basically meaning "all airports around Oslo". Some booking engines support these for convenience - for example, ones using Sabre as a backend may support QSF (also listed in this file) for all airports around San Francisco. I flew to Oslo recently and know I saw OSL used as a metro code first on at least one booking engine. It doesn't really make sense to put these in a list of physically visited airports but I wouldn't expect most people to know the intricacies of IATA codes.

Why it's designed this way with namespace collisions, I have no idea. Technically QSF also is a tiny airport in Algeria.

[compsciphd]

I'll be pedantic and say that technically OSL as a metropolitan city code isn't an airport (i.e. should fall under the same caveat as the railway portion of the man page)

[gspr]

Wow, TIL, and I stand corrected! That's crazy!

[reaperducer]

See also: NYC for metropolitan New York airport, and HOU for Houston's airports, even though Houston Hobby Airport is also HOU.

[gspr]

> NYC for metropolitan New York airport

Sure, but NYC isn't also a specific New York City airport (JFK, EWR, LGA). The problem here is that OSL is apparently used both for the metropolitan area and for one specific airport (in the metropolitan area).

[reaperducer]

I guess you missed the second half of the sentence you quoted. Where I note that Houston, the city, is HOU; and the Houston airports include IAH, EFD, and HOU.