Changing Planet

Where scale permits

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
The Geographer
Director of Editorial and Research
National Geographic Maps

Juan José Valdés is The Geographer and National Geographic Maps' Director of Editorial and Research. He guides and assists the Map Policy Committee in setting border representations, disputed territories, and naming conventions for National Geographic. As NG Map's Director of Editorial and Research, he is responsible for ensuring the accuracy and consistency of its maps and map products.
  • Dr Virginia R Hetrick

    One point that could help explain scale is an exercise wherein people go to the main page of google maps which displays the US, southern Canada, and northern Mexico, if being viewed in the coterminous 48 states. But, when clicking on the location of our hometowns several times, increasingly detailed information appears, according to the current scale of the map. It is also interesting to note that sometimes the level of detail is such that it is impossible to orient one’s self at the particular scale, so the user has to zoom out to some degree to find out where s/he is with respect to things like freeways, off-ramps, major arterials, etc.

    • Juan Valdes

      Dr. Hetrick:

      Point well taken.

      Dynamic mapping applications, such as google maps, have done much to improve cartographic literacy.
      Simple exercises, such as the one you’ve noted, is but one method.

      Thanks for sharing.

      Juan José Valdés
      The Geographer
      Director of Editorial and Research
      National Geographic Maps

  • Rand Myrick

    Mr. Valdes,

    I have an idea that will make maps more interesting. There should be descriptions of how a name on a map (canyon, creek, peak, etc.) got its name. For instance if a canyon was named Horse Thief Canyon on a map, there should be a description of why it was named Horse Thief Canyon. This could be detailed in a book or somewhere. Popular hiking or off-road areas like the Grand Canyon, Adirondacks, areas outside populated areas, etc. could be the first to detail. People and tourist in the area would love to know the background of the area and would love to have these maps.

    I could spearhead this by speaking with people in the community and putting this toghether as a sample of what could be. There are key people in every community that have this knowledge of why a place was named what it was. This information is not being passed on to it’s next generation and will be lost if we do not do anything. Please let me know if this is something you may be interested in.

    Thanks for your consideration.

    Rand Myrick


    Durango, CO

  • Ian Allan

    Congratulations Juan. Great article. I would like to add a couple of points.

    For surveyed features such as roads, scale is very much about the ratio you talk about. However for thematic mapping scale is often also about the scale of collection as well as the scale of publication. In particular, for natural features its about how many days in the field back up the theme that’s being mapped.

    Also, something that concerns me. Many times I have seen paper maps finding their way into a Geographical Information System. More often than not the cartographer’s art gets lost and the maps find themselves being used for purposes and at scales other than those they were intended for.

    Ian Allan

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