Maps in Journalism

Scale, Distortion, and Generalization

Maps work by condensing information about places and distances into comparatively small, highly generalized graphic representations. The ratio of map distance to ground distance is called scale. Sheet maps and atlas maps typically report their scale as a ratio or fraction such as 1:24,000 or 1/24,000, which means that an inch on the map represents 24,000 inches, or 2,000 feet, on the ground. Small-scale maps, with relatively small fractions like 1/100 million, require considerable generalization to reduce a large country, a continent, or the entire world to a display less than a foot wide. By contrast, a large-scale, 1:2,000 newspaper map two columns wide can show individual land parcels on a city block. Because viewers might not readily grasp ratio scales, large- and medium-scale news maps typically state their scale graphically, with a horizontal bar perhaps a half-inch long and a label indicating the corresponding distance. Bar scales on news maps generally represent a single distance, always in miles in American newspapers.

However appropriate on maps of neighborhoods or states, bar scales are potentially misleading on small-scale maps, where scale varies significantly from place to place as well as with direction. Flattening the spherical earth is a complex process, which requires drastic distortion of distance and shape. (On a rectangular world map, with a grid of evenly spaced meridians and parallels, north-south scale is constant while east-west scale approaches infinity near the poles—stretched from mere points into lines as long as the equator.) Although stretching is unavoidable on large-scale maps of neighborhoods or counties, geometric distortion is not noticeable if the map author selects an appropriate map projection. These maps are typically framed with a conformal projection, the type used for topographic maps and nautical charts. Because scale at a point is the same in all directions on a conformal projection, circles and complex curves can retain their characteristic shapes. And because the area shown is not large, distances and areas are not noticeably distorted. By contrast, conformal projections like the Mercator, used for nautical charts to portray constant sailing directions as straight lines, are not recommended for small-scale maps, on which they can severely distort area. The classic example of an [Page 869]inappropriate map projection is the widely used Mercator world map, which portrays Greenland as roughly the same size as South America. Numerous projections suitable for whole-world or continental maps either preserve relative area or offer an appropriate compromise between distorted areas and distorted shapes and angles.

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