In a correction to the size of Beach City in Blue Mars the size is 4,000 x 4,000 meters or about 16 square kilometers. The upper limit is 8,000 x 8,000 meters for a whopping 64 sq kilometers! Here I am on the western side of the Beach City map looking east towards Diamond. You can just barely make out the roof of the hotel.

FYI, there are two levels of developers: City developers who invest in a city and Block developers who work in an area about 65,000 square meters (the size of a sim in SL) .