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Introduction to GIS - ISRPlatoon

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					Map Scale


Laurie Garo
Geog 2103: Intro to GIScience &
  Technologies
Fall 2012
Outline
¡   What is Scale?
¡   Representation of Map Scale
     l Map Scale Ratio

     l Large vs Small Scale

     l Area Coverage vs Detail

     l Scale Variance

¡   Representative Fraction
¡   Verbal & Graphic Scale
¡   Scale in GIS
    What is Scale?
¡ “Scale is the amount of reduction that takes
  place in going from real-world dimensions to the
  new mapped area on the map plane” (Dent,
  1999, pg. 11)
¡ Scale influences area coverage and level of detail
  (on a given page size)
¡ Scale helps us differentiate relative sizes of areas

¡ Scale enables us to make measurements on maps
Representation of Map Scale
l   Map Scale Ratio:
l   1 / scale = map distance/ground distance
l   Where 1 unit on map represents xx units on the
    ground
l   Must be same units (inches:inches;
    centimeters:centimeters)
l   Examples
     ¡ 1:2000      1”on map rep. 2000” on ground
     ¡ 1:24,000

     ¡ 1:50,000

     ¡ 1:63,360 (note: 63,3360” = 1 mile)

     ¡ 1:100,000 (note: 100,000 cm = 1 km)

     ¡ 1:3,500,000
    Large vs Small Scale
¡ Large Scale: less land area in more detail
¡ Denominator is a smaller number

¡ Small scale: more land area in less detail
  (generalization of features)
¡ Denominator is a larger number

¡ 1: 24,000 or 1: 3,500,000 which is larger
  scale? Which shows more detail?
¡ ArcGIS examples
Scale Variance
¡   Scale is true at the center of a map
¡   Scale varies as one moves away from the
    center towards the edges
¡   Large Scales required for precise
    measurements
¡   Small scales used when comparing
    distributions without need for measurement
¡   Generally: 1:24,000 and larger = large scale
¡   1:50,000 to 1:250,000 = medium scale
¡   1:1,000,000 and smaller = small scale
Representative Fraction Calculations

¡   RF of 1:80000; MD = 8.5”; GD? mi.
¡   RF of 1:250000; MD = 13.5 cm; GD ?km
¡   RF of 1:35,000; GD = 1500 ft; MD ? in.
¡   RF of 1: 28,000 ; GD = 850 m; MD ? cm
¡   MD = 7.5”; GD = 400 mi; RF?
¡   MD = 15 cm; GD = 600 km; RF?

¡   Conversions:
¡   63360 in. = 1 mi;     100000 cm = 1 km
¡   12 in. = 1 ft.; 100 cm = 1 m
Verbal Scale
¡   Representation of scale as 1 inch represents
    so many feet or miles; 1 cm represents so
    many meters or kilometers
¡   1:3,500,000     How long to drive 3,500,000
    inches?
¡   Divide denominator by 63360 for miles, 12
    for feet; 100000 for kilometers; 100 for
    meters
Verbal Scale
¡   3,500,000 / 63360 = 55.2399 miles therefore 1 ‘
    rep. 55.2399 miles
¡   More user friendly
¡   How long to drive 55 miles?

¡   3,500,000 / 100000 = 35 therefore 1 cm rep 35
    km
¡   24,000 / 12 = 2000 or 1” rep 2000’
¡   24,000 / 100 = 240 or 1 cm rep 240 m
    Graphic Scale
¡   Graphic representation of combination of RF
    and Verbal
¡   Line length drawn to represent feet/m (larger
    scales) or miles/km (smaller scales)
¡   Line length need not be exactly 1”
¡   Distance represented should be an even
    number for ease of measuring
¡   1” = 55.2399 mi. 1.0862” = 60 mi. (60/55.2399
    = 1.0862)
¡   Automatic in ArcGIS (guided demo)

				
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posted:4/11/2014
language:English
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