The admin can allocate VERY huge pieces of land. The Gallery server, for example, has galleries set up for some 20 x 1000 areas, which should be more than enough. This is done in the settings, using the size of the gallery. This is the gallery definition from the Gallery server for the Desert gallery:
{ -- Name of the gallery, as used in the commands Name = "Desert"; -- Name of the world for which the gallery is defined. WorldName = "world"; -- Dimensions of the gallery MinX = 100; MinZ = 100; MaxX = 500; MaxZ = 20000; -- The schematic file that will be used to initialize new areas within the gallery AreaTemplate = "gal/desert.schematic"; -- Edge of each area that is "public", i. e. non-buildable even by area's owner. -- This is so that the AreaTemplate may include e. g. sidewalks that will be preserved -- Setting this to N means that N blocks from each area's edge are protected, i. e. sidewalk of width 2 * N AreaEdge = 2; -- Strategy used for allocating the areas in the gallery. -- Represents the direction and the order in which areas are allocated out of the gallery -- "x+z+" means first increment X, then (when MaxX is reached) increment z and start over with x from MinX. -- Other possible values: "x-z+", "x+z-", "x-z-", "z+x+", "z+x-", "z-x+", "z-x-". FillStrategy = "x+z+"; -- The biome to set into areas in the gallery Biome = "Desert"; },Note the MinX / MaxX / MinZ / MaxZ coordinates, and note that the areas are 20x20 blocks in size (based on the .schematic file).