In my world, I created the very first map and went traveling to map out the world. Once my dad and brother crafted their blank maps, they both made exact copies of mine, all named map #0. I expected their maps to be blank and that they would both have to go and cover ground/map things out themselves.

The map on the left in the first inventory slot is my original map. The map on the right in the ninth inventory slot is my brother's map. You can see that though both maps are selected, they are in fact identical.