An example of this would be Kotar, home to Tuzluka City.
Middle worlds occupy the range between undeveloped and fully developed urban sprawl. Kotar is considered a 'lower-middle' because of only having really one large city.
After a world is colonized, the natural resources there determine how much it will be developed. Agrarian worlds are typically left similar to Kotar, with a handful of large cities. However, precious minerals and other valuable resources bolster a world's chances of becoming highly industrialized and ultimately urban.
Technology is incredibly expensive so middle worlds are typically told to either set up their own factories for refinement, or use their own resources. As such most middle worlds have a 'good enough' mindset. There is far more luxury than the Wilds but human labor is still much cheaper than building mechanics and robotics. As in Kotar, draft animals are often used. Garments are usually sewn at home, and factory space is usually reserved for tools of immediate need. Most of the exports from middle worlds are resources that have been initially refined from the raw resources of lower worlds; these then are exported to upper worlds where they are refined into advanced technology.