Please excuse this dumb question from a non-industry ignoramus.
Why are there two airport code schemes in existence? The ones that I know best are the 3-letter ones like LGW, LHR, etc. But I've also noticed that pilots often use the 4-letter ones like EGKK and EGLL.
I'm guessing that EG is for English airports, and so this system must also be an international one (presumably other countries use other two-letter prefixes).
So, why are there two schemes? In what different circumstances are the two schemes used? Is one just for us plebs and the other for pilots? Is it to do with map symbology?
Enquiring mind wants to know
