Is it possible to change city size in SimCity? I heard many people complaining about being 2km x 2km, but don't know if somebody has done a trick or if Maxis is going to change it?
No, it is not possible to change the city size.
You cannot increase the city size and play on EA servers today.
Creative Director Ocean Quigley says SimCity’s team “could certainly make the city sizes larger” as a reaction to more powerful hardware setups. ... "We’ll eventually get around to expanding the city size, but I can’t make any promises as to when.”
Also, it's possible to make a mod to enable debug mode. This allows one to build outside the city boundary.
In my opinion, the current size of the map (16x16 HD buildings with streets between them) just needs to be doubled in both directions (32x32 HD buildings with streets between them).
Looks like this guy is able to change the size of the map.