demap.el adds a minimap that shows a zoomed out view of the active window's
buffer. You can toggle showing the minimap in a side window with
"demap-toggle". This package has a few advantages over other minimap
packages: support for detaching minimaps and having them on a different
frame then the active window; support for multiple minimap buffers, with
their own buffer local definitions on what buffers it can show and how to
show them; having the minimap on the side of the frame rather then on the
side of the active window by default.