Michael,

National Library of Australia has been putting indexes online via its catalogue for some years.
These are drawn in Coreldraw, using a scan of a blank index, or a hand-drawn index (using vector outline maps).
A paper copy is printed at A4 (A3, A2 or even A1 for larger indexes), and attached to the first folder of the series in the drawer, and also housed in ringbinders in the reading room, for rapid consultation (we have also indexed some series that are not yet catalogued, hence another reason to maintain the reading room's hardcopy set).

Once a map series is scanned, we can then make the index interactive: clicking on the pink squares indicating held sheets, one is taken directly to the scan of that sheet (or sheets, if multiple eds are held).
For interactive indexes, the viewer also has arrowhead buttons in 8 directions, to allow movement directly from the image of one sheet to the image of any orthogonally/diagonally adjacent sheet, without needing to step back out to the index.
When you do step back out, the sheet you were viewing is highlighted in yellow on the index.

We have about 3000 such series indexes online,
https://catalogue.nla.gov.au/Search/Home?lookfor=%22map+index+at+national+library%22&type=all&limit%5B%5D=&submit=Find
Over 1200 of these series have also been digitised
https://catalogue.nla.gov.au/Search/Home?lookfor=%22map+index+at+national+library%22+%22digitised+item%22&type=all&limit%5B%5D=&submit=Find
and many of those have now been made interactive
e.g. https://nla.gov.au/nla.obj-942566394/view#
https://nla.gov.au/nla.obj-233457883/view

All digitised maps can be freely downloaded as 600dpi tif (some scanned >6 years ago and not yet rescanned are still 400dpi or 300dpi)
I'm more than happy to share blank copies of any of our indexes.

Brendan Whyte
National Library of Australia