National Library of Australia uses LC G-schedule for classification (Gimme a G!)
We also use folders.
We sourced flat card 1300x1800mm from memory) from a company in England who would cut it to size... we could only get a roll of card locally and would have had to cut it ourselves. It's fairly stiff, so you can pull out a full folder and carry it without it flopping too much, and fairly smooth, so multiple folders slide in and out easily.
We fold the sheets in two and they fit our drawers, or we cut the sheets in half and fold the halves for smaller topo series (US 24k, NATO 50/100k etc).
Number of maps per folder depends a lot on weight and weight on paper stock (photo maps on heavier paper vs line maps on thinner paper).
Our collection is not open access, so with only staff handling items, we can shove more in a drawer, especially low use items.
I prefer 3 folders (or 6 half-sized folders in two piles of 3) per drawer.
For less-full drawers, you can riffle through a folder to find the map you want and pull it out ; for fuller drawers you can extract the folder (to a nearby open drawer, the top of the cabinet or a nearby table) and extract what you need, then refile the folder.

I attach an A4 document pocket to the front of any topo series folder (first folder only for a multi-folder series) and insert a paper copy of our coloured series index (a digital copy is also attached to the record).

We flatten most maps. Older, dissected map mounted on cloth and sold in a slipcase are left folded, as are maps with heavy covers.
Anything too big to go in a drawer flat, is generally rolled onto a cardboard core, and housed in a triangular tube. Not space efficient, but easier to handle. We don't make folds in large flat maps just to get them into a drawer.

Tiny maps (those small CIA ones) I tended to put in a small mylar pocket, so they didn't get lost in the folder among their larger cartographic brethren.

University of Melbourne used heavy weight transparent polythene bags instead of folders, which made visual inspection easy. They also used Boggs & Lewis classification as did most of the state libraries.



Brendan Whyte