Complex sentence: Mayapan is 4.2 square kilometers and has over 4000 structures most of them residences, are packed into this compound within the city walls, while built-up areas extend a half kilometer beyond the city walls in all directions.
Split into simpler sentences: Mayapan is 4.2 square kilometers and has over 4000 structures, most of them residences, packed into this compound within the city walls. Built-up areas extend a half kilometer beyond the city walls in all directions.