What is a Document Map (aka minimap)? Look here, for example:
https://notepad-plus-plus.org/features/document-map.html
or here:
http://geekswithblogs.net/sdorman/archive/2008/08/30/document-map-margin-in-visual-studio.aspx
or here:
MiniMap: The MiniMap is a zoomed out graphical rendering of the active document. This allows the user to keep perspective inside the opened document, while also giving the editor a quick and efficient means of traversing and navigating the document. The MiniMap gives you a quick idea of which part of the document you are looking at.
This would be very useful!