Antique pocket maps, frequently called folding maps, occupy a special niche in the map-collecting world. During the 19th century in the United States, these little booklets were frequently carried by emigrants travelling across an unknown continent. Due to their physical format and frequent folding, pocket maps had a low survival rate. Today, they stand at the intersection of antique maps and ephemera. Some of the most important and rare maps on the market today are pocket maps.