I think they just had the one map for the beta. There's apparently terraforming tools that come with it too, so you can make your own maps.hughobrien
There is no terraforming, and the map sizes are fixed at the same size as all the videos you've seen. This has been a major complaint for many people. I personnally think the game is rich enough on the simulation level to overcome that drawback, having played the beta for many hours. Unfortunately, I am not a representative sample of the entire community.
There is some good news, though. There have been many implications that development will continue on SimCity if the initial sales and community responses are good. Ocean stated in an interview that there was a trade-off they needed to make regarding city size versus simulation depth and quality early in the game's development. They chose simulation... and the quality of that decision is very apparent when playing the game. Ocean also stated that increasing city size would be easier to do later under post-release development conditions than trying to improve the simulation engine... He never explicitly stated they planned on increasing city size in a later expansion/patch, but the evidence is pointing toward that outcome. *crosses fingers*