Joshua 13 is a description of Israel’s physical inheritance of the Promised Land. Two and a half tribes receive the land that is on the Eastside of the Jordan River and nine and a half tribes receive a plan for the distribution of the land on the Westside of the Jordan River. So the Eastside receives the land and the Westside receives a plan.
Joshua chapter 12 is basically a transitional chapter in the book
that helps to move the narrative from one major section of the story to the
next. It’s kind of like a bridge from one main body of land to the next main
body of land. It can be helpful if you can envision yourself standing on the
middle of that bridge looking back at the land you just left with an eye
towards not only what lies behind you but also what lies ahead of you.