Some maps, particularly those of explorers, are the earliest to depict an area or feature. Other maps might depict an important battle or similar event. Other examples may be imagined geography such as California as an island. Generally the closer such maps date to the event the more importance and thus value they have. Generally the larger the map the more opportunity for detail and decoration.
Some maps are very large and difficult to display, reducing their value.
Some maps were issued in small numbers and are relatively rare. If other conditions that enhance value, are present the map is further enhanced by rarity, but rarity alone does not create value. For similar maps the older is generally the most valuable but age alone does not determine value as some very early maps of regions of relatively little interest have relatively little value. Age, like rarity, is more an enhancement of value. Some early maps were enhanced with large cartouches, sea monsters , ships and other decorative additions.