What is that feature called that shows a picture of the entire contents of the file on the right-hand side of the editor and shows it very small like it's zoomed out and shows the part of the file that is currently showing in the editor in a different shade in the picture? I am describing this to the best of my ability. I hope it comes across clearly.
How to turn on feature in Xcode Editor
This is called the "Minimap".
The menu for this in on an icon at the top-right of Xcode... (the middle of the three lower buttons, in the screenshot.)