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Fundamentals of GIS
Scale
To show a portion of the Earth's surface on a map, the scale must be sufficiently adjusted to cover the objective. Map scale or the extent of reduction is expressed as a ratio. The unit on the left indicates distance on the map and the number on the right indicates distance on the ground. The following three statements show the same scale.
1 inch = 2.000 feet => 1 inch = 24.000 inches => 1:24.000
The latter is known as a representative fraction (RF) because the amounts on either side of the colon are equivalent: that is 1:24.000 means 1inch equals 24.000 inches or1 foot equals 24.000 feet or 1 meter equals 24.000 meters and so on.
Map scale indicates how much the given area has been reduced. For the same size map, features on a small-scale map (1:1,000,0000) will be smaller than those on a large-scale map (1:1,200).
A map with less detail is said to be of a smaller scale than one with more detail. Cartographers often divide scales into three different categories.
Small-scale maps have scales smaller than 1 : 1,000,000 and are used for maps of wide areas where not much detail is required.
Medium-scale maps have scales between 1 : 75,000 and 1 : 1,000,000.
Large-scale maps have scales larger than 1 : 75,000. They are used in applications where detailed map features are required.
So each scale represents a different tradeoff. With a small-scale map, you'll be able to show a large area without much detail. On a large-scale map, you'll be able to show a lot of detail but not for a large area. The small-scale map can show a large area because it reduces the area so much that the large-scale map can only show a portion of one street, but in such detail that you can see shapes of the houses.
To convert this statement to a representative fraction, the units of measure on both the sides being compared must be the same. For this example, both measurements will be in meters.
To do this:
- Convert 1.6 inches into meters
1.6 inches x 0.0254 meters/inch = 0.04 meters
- Let us suppose that
0.04 units on the map = 10,000 units on the ground
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