The first suggestion is just to implement a way to find the center of a filled map in your hand.
The other suggestion is a bit more nuanced. Treasure maps use a map_decorations list in the NBT to mark where the treasure is. However, the symbols are loaded from the item into the map ID, so if you load thousands of map decorations onto a copy of a map, it'll apply to every other copy of the map until the server reloads -- INCLUDING maps that are in other worlds. So you could put thousands of symbols onto a map billboard at a server's spawn from their creative world, for instance. So you can effectively create lag bombs in areas that are protected, without even building there or being in the same world. It also seems to bypass certain protective measures servers employ to prevent items with wacky NBT being spawned in using creative hotbar loading.
Below is an example of a map depicting an ocean, covered with hundreds of jungle temple symbols. This can easily go into the thousands or higher and has a significant impact on FPS.
