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How to Use a Map Page 3
Measuring Distance
As stated earlier, the scale of the map determines how much of the earth's surface is covered by a particular map sheet. In the case of the 1:24,000 scale, a distance of 1 inch on the map equals 24,000 inches (2000 feet or .38 miles) on the ground. So, measuring the number of inches between two points on the map can be converted to feet on the ground by multiplying the number of map inches by using this formula:
ground feet = map inches x 24,000 12
example: 2.5 map inches = 5000 feet
(2.5 x 24,000) = 60,000 = 5,000 feet 12* 12*
*The 12 comes from the fact that there are 12 inches in one foot.
An easier way to measure this distance (without math) is to take the measurement (2.5 inches in our example) and transfer that measurement to the bar scales. If you want the distance in feet, use the feet bar scale, miles for miles and kilometers for kilometers.
Take a close look at the feet bar scale. You will see that is does not start at zero, but at 1000. Move to the right on the scale and you will get to zero, then to 1000, 2000, and so on. The distance between the 1000 and zero is 1000 feet. The most left portion of the scale is subdivided into five smaller section. Each of these is 200 feet. The distance between the zero and the 1000 toi the right is also 1000 feet, but it is not subdivided. The distance between the zero and the 2000 is 2000 feet, and so on. To make an accurate measurement, use a small strip of paper, and mark a distance between two point on the map. Take this measurement to the bar scal and put the right tick mark on the farthest right 'even-thousand' mark, while keeping the left tick markon the left sideof zero. In the case of a 2.5 inch measurement, the right tick mark would be on the 2000 point on the barscale, and the left tick mark would be exactly in the middle between the 1000 and zero on the left. In the smae way as you measure the distance between two objects on the map, you can also determine the area a certain distance from an object, by transferring the bar-scale measurement to a piece of paper, putting a tick mark on the object (such as a hilltop or a road intersection, and looking at where the second tick mark lands. Bear in mind that the aboe description are straightline distance, or "as the crow flies." Measuring walking distance or curves takes a different technique we'll talk about later.
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