Planar Coordinates

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Planar Coordinates

• Planar coordinates used more often
• They relate better to flat maps
• Mathematically simpler for calculating distances
  and areas

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Coordinates

• Planar Coordinates
• Perpendicular x and y axis with an arbitrary
  origin
• If geographic
• Eastings are x values
• Northings are y values

3
Coordinates

• Moving south and west results in negative
  coordinates
• Use false origin located outside of the mapped
  area
• False Easting
• False Northing

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Planar Coordinate System

• Easier to do distance and other calculations
• Use Pythagorean Theorem

5
Planar Coordinate System

• Two most widely-used coordinate systems in the
  United States
• Universal Transverse Mercator (UTM)
• State Plane Coordinate System (SPCS)

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UTM

• Universal Transverse Mercator
• Widely used for topo maps, satellite images, etc.
• Based on Secant Transverse Cylindrical Projection

7
UTM

• Divided into 60 zones, each 6 degrees of
  longitude in width
• Zone 1 starts at 180 mark, increasing eastward
• Zones extend from 80 south to 84 north

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UTM

• Each zone has a central meridian in the middle of
  each zone

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UTM

• Each zone has two parts a northern and a southern
  half
• Distance Unit -- meters

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UTM

• Distance from Origin is measured in Northings and
  Eastings
• X-origin is west of zone (a false easting)
• Central Meridian has an easting of 500,000 meters

False Origin
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UTM

• For Northern half of zone y-origin is equator
• Northing at equator is 0m
• For Southern half of zone y-origin is 10,000,000
  meters south of equator (80 S)
• Northing at equator is 10,000,000m

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UTM
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UTM

• Many study areas cross UTM zones
• Not very appropriate for areas much wider than 6
  of longitude
• latitude dependent
• It is possible to assign coordinates to more
  predominant zone

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UTM
15
UTM

• What do you do when your study area crosses the
  Equator?
• North zone Equator is 0m
• South zone Equator is 10,000,000m
• 0 ? 10,000,000
• One solution
• assign all coordinates to South zone
• dependent on area and extent

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UTM