Note: This is part of the setting of the world that our Steampunk personas come from, which is also content for the game we are working on.
Inner Rocks and Outer Rocks are not designated by where they are located. They are designated by its people and the governing body. Inner Rocks have well established colonies with a strong governing body, an established monetary system, and stable trading. The Inner Rocks have different government styles and different laws.
The Outer Rocks are often uninhabitable. Those that are habitable, may be used for farming, mining, or privately owned. Other Outer Rocks have colonies of people without a form of government, or perhaps an unfavorable or unstable form of leadership. They may be struggling for food and water, or plagued with disease. Some Outer Rocks may be hot spots for Diesel Pirates (more to come on that topic) and other forms of hostility. The Outer Rocks are simply undesirables, uninhabitable, privately owned, or just unclaimed.
Perhaps there are some Outer Rocks worth finding and converting to an Inner Rock; but they are hard to find and often fought over.