As is frequently the case, National Geographic mapmakers―for that matter, mapmakers worldwide―often face the problem of having to fit too much cartographic information into too little cartographic space. Scale, which defines the mathematical relationship between linear measurement on a map to that on the Earth’s surface, ultimately determines how much information can be portrayed on a sheet of paper or on a computer, ipad, or iphone screen.
For large-scale maps, as that of Downtown Boston, where the map to ground ratio is small, land areas can be mapped in detail―there is sufficient space for just about every major feature within its coverage area to be shown. However, as the map to ground ratio increases so does the map’s level of generalization. That’s why world maps, as illustrated by a section of the northeast coast of the U.S. (at left), can only portray a generalized, but somewhat comprehensive, view of the Earth.
Contentwise, cartographers are most challenged when map to ground ratios begin to increase. Decisions need to be made as to which elements will be retained and which will be set aside. Selecting which populated places to show on a map is always problematic, especially for well known areas. Here, and as a general rule, the most politically significant and largest populated places are selected and shown. Places of lesser importance or population are selected only if space―a.k.a. scale―allows.
“Where scale permits” has always been part of our mapmakers lexicon. Scale has and will continually dictate how detailed or generalized any map can be.
Juan José Valdés
Director of Editorial and Research
National Geographic Maps