Geography Reference
In-Depth Information
25,000 cm on the ground. Divide by 100,000 (the number of cm in a km) to
determine the statement of scale “1 cm equals 250 m or a quarter km.”
Scale Transformations
GI, whether collected in the field, collected from existing geographic infor-
mation, or digitized from existing maps, can be readily transformed to other
scales. The scaling of geographic information may be helpful for many rea-
sons. Most often, scale transformations allow the association of any arbitrary
coordinates from known places—for example, building corners or street
intersections—to be associated with coordinates of the same places in other
coordinate systems. In this way, locations of things and events drawn on a
piece of paper can be transformed into geographic information using a coor-
dinate system.
Scale transformations allow for an infinite number of alterations to
shapes and changes. They can change all axes by the same factor, each axis
by different factors, locally vary the transformation values, or use logarithmic
factors. These different types of scale transformations are necessary to sup-
port the different type of changes to coordinates required when working
with geographic information from different sources.
Several things need to be considered for working with scale transforma-
tions. First, it is important to remember to keep using the same units
throughout the transformation. Geographic information locations stored in
TABLE 5.2. Representative Scale
and Equivalent Ground Distances
Scale
Ground Distance
Standard (inches)
1:2,400
200 ft
1:20,000
1,667 ft
1:24,000
2,000 ft
1:62,500
approximately 1 mile
1:63,360
5,280 feet (exactly 1 mile)
1:125,000
approximately 2 miles
1:800,000
approximately 8 miles
Metric (centimeters)
1:1,000
10 m
1:2,500
25 m
1:10,000
100 m
1:25,000
250 m
1:50,000
500 m
1:100,000
1,000 m (1 km)
1:250,000
4,000 m
1:500,000
50,000 m (5 km)
1:1,000,000
100,000 m (10 km)
1:2,000,000
200,000 m (20 km)
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