Looking through several published airline timetables, there seem to be several cities that are listed with a different 3 letter code than the real 3 letter code for the city's airport. Some examples include:

New York: NYC versus JFK/LGA
Toronto: YTO versus YYZ
Jakarta: JKT versus CGK
London: LON versus LHR/LGW
Paris: PAR versus CDG

One would think that carriers would use the correct airport code for destinations they fly to published in the timetables which they do for most such as LAX, SFO, YVR, HKG, SIN, KUL, etc. But for New York, Toronto, Jakarta, London, and Paris the 3-letter NYC, YTO, JKT, LON, and PAR would be used respectively instead of JFK/LGA, YYZ, CGK, LHR/LGW, and PAR respectively. Have no clue as to why they would opt for something like that.

These are metro airport codes. So, LON means LHR, LGW, LCY, STN, LTN, MSE (and possibly SEN, I can't remember). Handy if, like me, you don't really care which airport you go from.

And NYC includes EWR.

It makes perfect sense to have a collective code for airports serving the same town. If you want to look up connections from London (any airport) to New York (any airport) you type LON-NYC and it gives you the lot. Much easier than having to look them all up individually.

Furthermore, I understand that the collective code is used for fare calculations which means that a flight to LHR returning from LGW is classed as a point-to-point return flight rather than an open jaw.

There are, of course, some anomalies in this... LGW and STN, both "London" airports, are further from each other than LGW is from SOU or STN is from NWI

I would find it much easier to get flight/fare info from Chicago to New York just by inputing a request for CHI-NYC just once and getting all flights/fares. Otherwise, I would have to input seperately ORD-JFK, ORD-LGA, ORD-EWR, MDW-JFK, MDW-LGA and MDW-EWR. (I'm not sure if they're included in the NYC designation, but also ORD-HPN, MDW-HPN, ORD-ISP and MDW-ISP.)

It just makes it easier.

I'm annoyed that there's no code for SFO/SJC/OAK. BAY seems to be available ...

As long as we're listing them, WAS=BWI/IAD/DCA

What about LAX/BUR/SNA (and maybe LGB)?

Depending on airline, one or the other works!

In FlyingFish (mileage calculating utility) only BJS works, and PEK returns a error msg!

anyone know if there is a Los Angeles generic airport code and a bay area generic code?

I think it's not used anywhere near as much as NYC, WAS and so on, but QLA can be used to cover the LA area airports- LAX, SNA, ONT, BUR and maybe LGB. It works on expedia.

Huh. ITA Software accepts both QLA and NYC; united.com accepts NYC but not QLA. I never knew about QLA. Is there an analogue for the Bay Area?

I've seen QSF, but it doesn't work as often as LON or NYC. I figured it wasn't a "proper" metro code somehow.

You can add MOW (Moscow) for SVO/DME.

YTO for Toronto includes YYZ (Pearson), The Toronto Island Commuter Airport (YTZ?), the train station (yup has its own code) and possibly Buttonville airport.