Metroplex is the Autobots' idea of a transforming city, where they are able to go about their business creating energy and helping the humans while fending off Decepticon attacks. In fact, Autobot City became the Autobots' new base on Earth after a time, leaving behind their non-transforming spaceship known as The Ark. As it turns out, Metroplex is not alone in the universe. Others sharing his body type have emerged in various fiction, and have come to be known collectively as "Metrotitans." Just imagine, an entire fleet of transforming robot cities, designed to rocket across the cosmos and help colonise alien worlds. The image above comes from the version seen in Transformers Animated, which (to anyone's knowledge) did not transform into a giant robot, but the design of the complex is basically the same as the original, save for a few details here and there. That said, here's a video clip to give you a sense of relative scale between Metroplex and his arch-enemy, Trypticon: