Mapping the Earth

1
Mapping the Earth
Geographic Coordinate System
Latitude Longitude
Degrees, Minutes, Seconds or Decimal Degrees
Universal Time
Projected Coordinates
Why Project a Map?
Types of Projections
Projection Issues
2
Geographic Coordinates
Latitude and Longitude

• Reference Grid covers the entire planet
• Latitude (Parallels) measured from the Equator
  (0º)
• North or South
• Never intersect
• Longitude (Meridians) measured from Prime
  Meridian (0º)
• East or West
• Intersect at the Poles

3
Latitude
Referenced to the North or South
North Pole 90º N
Arctic Circle 66º3338 N
Tropic of Cancer 23º2622 N
Equator Reference Line
Tropic of Capricorn 23º2622 S
Antarctic Circle 66º3338 S
South Pole 90º S
4
Longitude
Referenced to the East or West
Prime Meridian 0º
180th Meridian 180º
International Date Line
5
Measuring Latitude Longitude
Degrees, Minutes, Seconds

• A Circle can be broken into 360 Degrees (think
  of a compass)
• Each Degree is made up of 60 Minutes (of arc)
• Each Minute is made up of 60 Seconds (of arc)
• Greater Accuracy of Measurements

Decimal Degrees

• Mathematical conversion of Degrees, Minutes,
  Seconds
• Decimal portion is equal to
• (Minutes/60) (Seconds/3600)
• Example 23º 26 22 N
• 26/60.43333
• 22/3600.00722
• 23.44055º N

6
Time on the Earth
Time Zones

• The Earth is split into 24 Time Zones
• Time Zones are delineated around existing
  features

International Date Line

• Roughly the 180th Meridian
• Gain a day traveling West across the line

Universal Time

• Based on the time at the Prime Meridian
• Continuation of old Greenwich Mean Time (Zulu
  Time)
• Standardized time across the world

7
Projections
Why Project?

• The Earth is Round Maps are Flat
• No matter what is done, there will be error in a
  map
• Projections attempt to minimize the error
• Three kinds of error
• Scale (Size)
• Direction
• Area
• No Map can eliminate all error must find the
  best balance
• Depends on use

8
Projections
Basic Classes

• Cylindrical
• Conical
• Azimuthal

• Cylindrical Generally large, rectangular areas
• Conical Medium sized, triangular areas
• Azimuthal Small, circular areas

9
Projections
Mercator

• Common Projection
• Good for navigation
• Latitude/Longitude are all right angles
• Shapes are correct but size is distorted at the
  poles

10
Projections
Robinson

• Becoming more widespread
• Minimizes error no point is free of error
• Low distortion within 45 Degrees of center
• More realistic view of the entire world

11
Projections
Albers Equal-Area Conic

• Common projection for the United States (Lower
  48)
• Maintains proper sizes
• Shape errors increase away from center

12
Projections
Airy

• Azimuthal projection (circular area)
• Minimum-error projection
• Does not fully eliminate errors

13
Projections
Projection Errors

• Tissot Indicatrix
• French Cartographer
• Shows error in relative size and shape

Mercator
Robinson
Albers
Airy