Understanding Map Scale
Scale shows how many units on the ground are represented by one unit on the map. The scale with which we may be most familiar is called a graphic scale--a bar on which equivalent distances are marked off. A large-scale property survey might have a bar two inches long, with “0” at one end, “100 feet” in the middle, and “200 feet” at the end. Usually the scale is stated beneath the bar or graphic scale: “One inch equals one hundred feet.” The same scale may also be expressed by the fraction 1/1200, or by the ratio 1:1200. Each means that one unit of length on the map--inch, centimeter, or foot--represents 1,200 of those same units on the ground. One inch on the survey or map equals 1,200 inches on the ground, which in turn equals 100 feet, as described by the text under the bar.
Large-scale maps show the largest amount of detail of a small area. Typical examples are the USGS quadrangle maps, city and suburban street maps, and private property surveys.
Medium-scale maps have scales between a little over a mile to the inch and just under ten miles to the inch. Typical examples are highway maps of the smaller states and many nineteenth-century county maps and atlases. Where development was sparse, they may be all that's available and will provide the needed degree of detail.
Small-scale maps show a smaller amount of detail but cover large areas and allow us to orient ourselves and identify the locations where we will seek out larger-scale maps that provide more detail. Typical examples are world atlas maps and highway maps covering the larger states