noisms has an interesting post about a map created to scale of 1 mile = 1 mile. As suggested in his post, these map fragments could be a type of parallel world perfect for gaming. For me, it is a starting point to create unique gates, a new class of magic items, and a seed for "big bads" of all difficulties.
Here's the quote from Borges' One Exactitude in Science:
. . . In that Empire, the Art of Cartography attained such Perfection that the map of a single Province occupied the entirety of a City, and the map of the Empire, the entirety of a Province. In time, those Unconscionable Maps no longer satisfied, and the Cartographers Guilds struck a Map of the Empire whose size was that of the Empire, and which coincided point for point with it. The following Generations, who were not so fond of the Study of Cartography as their Forebears had been, saw that that vast map was Useless, and not without some Pitilessness was it, that they delivered it up to the Inclemencies of Sun and Winters. In the Deserts of the West, still today, there are Tattered Ruins of that Map, inhabited by Animals and Beggars; in all the Land there is no other Relic of the Disciplines of Geography.
Looking at any piece of the map (if you can unfold it) will help you navigate in the real world some of the time. The larger the piece, the more likely a PC will be able to use it to navigate. Let's say that if you take your piece of the map to the area it represents that a gate will open to a parallel world. Once characters travel through the gate, the map will change to represent the details of their new world. (This gives them a way back.) The downside is that the characters appear a random distance away from the place where they need to travel to reactivate the gate.
If the characters have an item from a parallel world, that item can help them travel to that world through one of these gates. It will require some divination magic to determine the path. I would set it as a second level spell (OSR/Swords & Wizardry) so that lower level characters will either be able to learn the spell fairly early in their careers or that it would be straightforward enough to hire the spell to be cast.
I have never liked Teleport spells, but in this world, higher level spells could teleport the caster from one point on the map to another. Again, this would work only when the caster is somewhere within the area represents by the map itself. To teleport any great distance would require a map larger than a horse-drawn carriage.
Doing some thumbnail calculations, a map made out of standard American 20 lb paper that displayed a square mile would weight about 3400 tons. Again, the material for the map would have to be much much lighter. In a way, this makes the back of map pieces valuable for anything requiring a lot of writing space. Imagine a spell book that is pages of magical formulas on one side of the paper, and a series of maps on the other side. In other words, take a spell book, and turn it over. Read from back to front to see a series of interconnected maps of a single room. (Each page is a little less than a square foot. A 100 page spell book would be about the same as a ten feet by eight feet room.)
Going back to the teleportation powers of the maps, let's say that a high spell level (4th or 5th) would allow the caster to teleport to the locale shown on the map. The caster would arrive anywhere within the area shown by the map. The risk in using the spell would be a chance that the caster arrives in a parallel world instead of his/her intended destination. Going back to the spell book made of paper from the great map, a wizard with his spell book could always manage to attempt to teleport to safety.
So let's set some definitions. The paper for the Relics of Geography looks like 20 lb modern paper but is exactly 1000 times lighter. One a small scale, that makes the 100 pages of a spell book weight 1/4 ounce. (The 3 lb weight listed in the d20 src must be the weight of the cover.) On a larger scale, a map showing a square mile weighs about 3.5 tons. This would require a team of three to six horses to pull. Folding the square map 17 times, should make it fit in a space that is roughly 20 feet by 10 feet, so it's a large carriage. Yes, it has to be many many times stronger than paper. It can still be stronger than anything, but easily cut.
I mentioned big bads earlier. These map fragments work to take things out of this world and to bring them in. Parallel worlds do not require any similarity at all to the standard campaign world. Considering the size of the entire map, pieces of the map are common enough that creatures of all kinds can travel around the multiverse looking for worlds that can be easily controlled and/or exploited. Since a spell is required to make use of the map fragments, the bad guys would most likely be intelligent.
Hopefully, more on this in another post. This was just too interesting to pass up. Thanks noisms! (Yes, visit his site. Always fun.)