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A mile is a unit of linear measurement that equals 5,280 feet. While most of the world has adopted metric units (kilometers), Americans continue to express distance in miles, which, therefore, commonly appear as units of measurement on maps made in the U.S. But exactly what is a mile? And why does it consist of 5,280 feet instead of a more convenient figure, like 5,000?

“Mile” comes from the Latin milia, meaning thousand. In Roman times, a unit of linear measure called the milia passum, or thousand paces, was common. Somehow, somebody’s thousand strides became a standard Roman mile, equal to about 1,650 yards. This measurement became widely used in Britain following the Roman’s invasion. After the Empire’s demise, however, the milia passum fell into disuse, although “mile” endured in the British vocabulary as a word applicable to a substantial distance.

The mile’s present length has its origins in medieval English agriculture. Back then, a team of oxen was used to pull a heavy wooden plow. The farmer walked behind, making liberal use of an ox goad — a big stick — to influence the animals’ behavior. The stick was known as a rod, and at some point its length was standardized to 16.5 feet. The length of a parcel of farmland was “a furrow long,” or furlong. That was the distance the oxen could pull the plow before the farmer had to stop and rest them. Naturally, that length varied. In time, however, the furlong was standardized to a distance of 40 rods (660 feet or 220 yards). Sometime later, a distance of 8 furlongs (5,280 feet or 1,760 yards) became the standard mile, and remains so to this day.

 In Figure 5-2a, 1 inch represents 630 miles. As a result, this map shows a comparatively large area that includes most of the Great Lakes, Upper Midwest, a handful of major cities, and a portion of Canada.

 In Figure 5-2b, 1 inch represents 190 miles. What is shown now is a much smaller area that includes parts of Lake Michigan and Midwest states, a few medium-size towns, and a few major regional highways.

 In Figure 5-2c, 1 inch represents 64 miles. Now we have “zoomed in” to the extent that the map shows Greater Chicago, southern-most Lake Michigan, more municipalities, local highways, and several streets.

Notice that as the area shown on these maps decreases, the amount of detail increases. And if you think about it, that makes a great deal of sense. When 1 inch represents 630 miles — a large area — only very large surface features (such as the Great Lakes) can be shown. But when 1 inch represents 64 miles — a much smaller area — then comparatively small surface features (such as roads) can be effectively shown.

(© John Wiley & Sons Inc.)

FIGURE 5-2: These three maps have different scales, and therefore differ in area and detail.

In the lingo of cartography, small-scale maps show large areas in little detail, while large-scale maps show small areas in big detail. Figure 5-2a has a comparatively small scale. In contrast, Figure 5-2b has a somewhat larger scale, while Figure 5-2c has the largest scale among the three maps. And indeed, as the scales of these maps get larger, the degree of detail increases. Calling the first map a small-scale map makes sense as the representative fraction, if actually divided, would result in a much smaller number than the other two maps.