flickr and the airport code

On my flickr profile page there's a fill-in for airport code - for what purpose, I don't know - but the closest airport to me is Canton-Plymouth-Mettetal Airport in Canton, Michigan. The airport code is 1D2.

Mettetal Airport Website http://www.mettetal.com/

Wikipedia http://en.wikipedia.org/wiki/Canton-Plymouth-Mettetal_Airport

Airnav information http://www.airnav.com/airport/1D2

FAA information http://www.airport-data.com/airport/1D2/