How is it that airports expand to meet higher demand?

[mthdscrd]

and would it be possible to apply the process to other zones? 
The reason I ask is because I live in an area undergoing a boom in residential development-it seems like every day another farm is being converted to housing, or a new drive is being added on to an existing one.  It would be cool to zone some low density residential that could then 'expand' to meet demand as long as it wasnt ringed by roads...

If you've already come across my idea in an other post i'm sorry for the repetition-i've thrown this idea out in a couple different threads...

[JoeST]

I believe only ports can "evolve" due to demand, and you have to remember that ports are static lots... it just interchanges the lot on upgrade (i guess...) whereas RCI develop in user created blocks that then develop...

Joe