Free cities come in 3 main categories, border towns, Depots, and sky cities. The Junction is the largest of the free cities.
Little towns on the borders between nations. They intentionally remain small to go unnoticed by either side and be left alone. Tight knit communities are formed and everyone looks out for each other. Because of this sense of community crime is very low. Often high walls are built to protect the town from the super predators that roam the wastes.
The Depots (with a capital D) are essentially one large multifaceted building, each rail road controlling a different part. Rival rail roads being in such close proximity to each other provides an environment ideal for spies and crafty smugglers.
Each rail line has its own security force and precautions against smugglers, items deemed perfectly acceptable on one line might be considered contraband on another. Areas between the gates of the different Lines tend to be unprotected by any form of security or rule of law, theft and assault while uncommon aren't unheard of in these areas. These spaces are also poorly maintained each rail road considering it to be someone else's responsibility.
The sky cities, drift above the dangerous wasteland. Using salvaged airship technology they are able to keep aloft nearly indefinitely. These towns as much out of a need to stay safe from the beasts on the ground as a desire to keep out of the reach of the recovering nations and the taxes that follow. The populations of these towns tend to be small close knit communities, some shun the outside world remaining isolated, while others welcome visitors and merchants. While dubbed "cities" the population of these towns tend to remain small do to lift and space restrictions.
Some of the Sky Cities have permanent moorings whether it be near a cliff, in a mountain pass, or anchored over a bit of farmland on the wild planes. Others remain un-moored using steam or diesel engines to travel general trade routes, or use sails moving completely at the whims of the winds. Those with moorings frequently make use of the little patches of land around their anchors, either through rough farming, or building trading posts for the merchant caravans that travel the wilds.