I would like to know what this approach is called. In case my incredibly high-fidelity mockups are too confusing, what I'm after is a design that explicitly links the thumb to the viewport by drawing a filled area linking the top of the thumb to the top of the content and the bottom of the content to the bottom of the thumb, thereby highlighting the connection between content and proportion of content visible compared to the total content available. I have seen various versions of this but can't put my finger on any.
[Edit] Just to be clear. Obviously I know what a standard scroll/viewport combo is and looks like. I'm after this variation which explicitly links content to thumb using a graphical device which in the case of my diagrams is the light grey polygon running from the edges of the content to the edges of the thumbnail bar.