This area is the place where all important offices and administrative buildings of the Hidden Mist village are located. Here you can find the office of the Mizukage and all of the other big shots, like Daimyo.
The Gates of Kirigakure no Sato, if you wish to enter the village this is the place where you must post first before going to some other area. If you plan to sneak in, be careful not to get caught.