Geography Reference
In-Depth Information
ing 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.
Representative fraction (RF)
The area shown on a map is a fraction of its actual size. Appropriately, therefore, scale may be
indicated as a representative fraction (RF), which states the ratio between a unit of distance
on the map and the same distance measured in the same units on the ground. As far as most
people are concerned, this is the most confusing scale-type and the most difficult to explain.
OK, here goes.
Check out Figure 5-1 again. The RF shown is 1:63,360. That means the map is 1/63,360th the size of
the area it shows. Stated differently, a distance of one inch on the map equals 63,360 inches on the
Earth's surface.
Once more, a given map has a given scale, but you can express it in different ways. In the example,
therefore, “One inch equals one mile” and “1:63,360” must mean the same thing. And, indeed, they
do.Proofisobtained bycalculating the number ofinches inamile. Todothat, multiply the number of
inches per foot times the number of feet per mile (12 × 5,280). The answer is 63,360, so the statement
of scale and the RF are, in fact, the same.
Comparing Earth at different scales
Maps come in different scales; and because they do, the amount of area and degree of detail
shown on one map may be very different from another. This is demonstrated in Figure 5-2,
Search WWH ::




Custom Search