• The video above is from the September 2012 iPad edition of National Geographic magazine.

    Choosing a map projection is a major challenge for cartographers. Features such as size, shape, distance, or scale can be measured accurately on Earth. Once projected on a flat surface, however, only some of these qualities can be accurately represented. Every map has some sort of distortion. The larger the area covered by a map, the greater the distortion.

    Depending on the map's purpose, cartographers must decide what elements of accuracy are most important to preserve. This determines which projection to use. For example, conformal maps show true shapes of small areas but distort size. Equal area maps distort shape and direction but display the true relative sizes of all areas. There are three basic kinds of projections: planar, conical, and cylindrical. Each is useful in different situations.

    Cartographers at National Geographic chose to use a version of the Mollweide projection for their map highlighting ocean floors, published as the map supplement in the September 2012 issue of National Geographic magazine. This Mollweide projection is referred to as a pseudocylindrical projection. The specific version of the Mollweide projection used is called an interrupted Mollweide, because lines of longitude, or meridians, are interrupted. The map is pulled apart at specific meridians to minimize distortion in areas where the cartographer would like the map reader to focus their attention.

    Find more interactive content, photos, and videos in the iPad version of National Geographic magazine.

  • Term Part of Speech Definition Encyclopedic Entry
    accuracy Noun

    condition of being exact or correct.

    bathymetric map Noun

    representation of spatial information displaying depth underwater.

    cartographer Noun

    person who makes maps.

    cartography Noun

    art and science of making maps.

    conformal map Noun

    representation of spatial information where angles, scale, and shape are preserved.

    cylindrical projection Noun

    map projection where the Earth's surface is projected onto a tube, or cylinder, shape.

    distortion Noun

    representation that is twisted, mistaken, or false.

    ellipsoid Noun

    shape of an elongated oval with some dimension of depth.

    equal area map Noun

    maps that show true relative sizes but distort shape and direction.

    Goode projection Noun

    representation of a sphere that does not distort land masses and divides spatial information into six unequal lobes. Also called an orange-peel map.

    longitude Noun

    distance east or west of the prime meridian, measured in degrees.

    Encyclopedic Entry: longitude
    map Noun

    symbolic representation of selected characteristics of a place, usually drawn on a flat surface.

    Encyclopedic Entry: map
    map projection Noun

    method by which shapes on a globe are transferred to a flat surface.

    Mercator projection Noun

    representation of a sphere where lines of latitude and longitude are straight and at right angles to one another.

    meridian Noun

    line of longitude, dividing the Earth by north-south.

    Mollweide projection Noun

    representation of a sphere where area is shown accurately but directions and shapes are distorted.

    navigation Noun

    art and science of determining an object's position, course, and distance traveled.

    Encyclopedic Entry: navigation
Tell us what you think