There are two main ways to indicate the scale of a map: graphic scales and fractional scales. Graphic scales use a bar graph to represent distances on a map versus actual distances on earth. Fractional scales express the scale as a ratio, such as 1:24,000, where 1 unit on the map equals 24,000 units on earth. To calculate distances using a fractional scale, the measured distance on the map is multiplied by the denominator of the fractional scale. This provides the actual distance in the same units, which can then be converted to other units of measurement.
Map Scale The scale of a map indicates how much the Earth has been reduced for reproduction on that map.
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In practical terms,scale is the relationship between the distance shown on a map and the actual distance that it represents on the Earth. Map Scale
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Ways to IndicateScale Graphic scales See figure 1 in lab manual Fractional scales Example 1:24,000 Graphic Scale There are two common ways to indicate the scale of a map:
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Graphic Scales Thegraphic scale of a map is a bar graph graduates by distance. Figure one in the lab manual shows the graphic map scale from a U.S. Geological Survey topographic map.
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To use agraphic scale, simply measure a distance on the map (or mark off the distance on the edge of a piece of paper), then compare the measured distance to the bar graph to determine the actual distance represented. Graphic Scales
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Graphic Scales Onsome graphic scales, “zero” is not at the far left, this is to make it easier to read fractions.
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Graphic scales areuseful since they remain accurate even if the map is enlarged or reduced. Graphic Scales
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Fractional Scale Thefractional scale or the representative scale expresses the scale of a map as a fraction or ratio. 1/24,000 or 1:24,000
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Fractional Scale: 1/24,000or 1:24,000 This scale, which is read “one to twenty-four thousand”, says that one unit of measurement on the map represents 24,000 units of measurement on the Earth.
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At this scale,one centimeter on the map represents an actual distance of 24,000 centimeters on the Earth, and one inch on the map equals 24,000 inches on the map. Units of measurement must be the same in both the numerator and the denominator. Fractional Scale: 1/24,000 or 1:24,000
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Computing Distances withFractional Scales Use a ruler to measure the distance on the map in inches (or centimeters). This is the measured distance . Multiply the measured distance by the map’s fractional scale denominator. This will give you the actual distance in inches (or centimeters). To convert your actual distance in inches (or centimeters) to other units, use the following formulas: To determine distances represented on a map by using the fractional scale:
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Conversions To determinethe distance in feet , actual distance in inches / 12 To determine the distance in miles , actual distance in inches / 63,360 To determine the distance in meters , actual distance in centimeters / 100 To determine the distance in kilometers , actual distance in centimeters / 100,000
Metric Measurements 1Kilometer (Km) = 1,000 meters (m) 1 Kilometer (Km) = 100,000 cm 1 Kilometer (Km) = 1,000,000 mm 1 meter = 100 centimeters (cm) 1 centimeter = 10 millimeters (mm)
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Examples If amap has a scale of 1/24,000, a measured distance of 8.25 inches on the map represents an actual distance of 198,000 inches 8.25 X 24,000 = 198,000 inches 198,000 inches / 12 = 16,500 feet 198,000 inches / 63,360 = 3.1 miles
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Examples If amap has a scale of 1/50,000, a measured distance of 22 centimeters on the map represents an actual distance of 1,100,000 cm 22 cm X 50,000 = 1,100,000 cm To calculate the actual distance in meters and kilometers: 1,100,000 cm / 100 = 11,000 meters 1,100,000 cm / 100,000 = 11 kilometers
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Large Versus SmallScale Maps Large scale maps refer to maps with a relatively large representative fraction such as 1/10,000. Large scale maps show a small area of the Earth in great detail. Small scale maps refer to maps with a relatively small representative fraction like 1/1,000,000. Small scale maps show large areas in less detail. Small Scale Medium Scale Large Scale