Laura Johnson
Cherie Aukland
NSF DUE-1205110;
0903270
GeoTEd Partners
Module name and number
NSF DUE-1205110;
0903270
Module Outline
 Methods of determining location
 Spatial Reference
 Coordinate system
 Datum
 Projection
Module name and number
NSF DUE-1205110;
0903270
What Is Our Location?
 The question: Where am I on the earth?
 Answers:
 Blacksburg, VA
 zip code 24060
 mile marker 118, I-81
 Worsham field: Latitude: 32.21997, Longitude: -80.41873
NSF DUE-1205110;
0903270
Where am I?
 All of the previous answered the question, but which
one will help me the most?
 All are forms of georeferencing, or communicating
location on the earth’s surface
NSF DUE-1205110;
0903270
Spatial Reference
 A way to communicate location that has up to three
components:
 Coordinate system (X, Y)
 Datum (accounts for shape of the earth)
 Projection (minimizes 3D -> 2D distortion in some
capacity)
NSF DUE-1205110;
0903270
Coordinate Systems
 Measure X, Y from an origin point
 Origin and units vary based on the coordinate system
 Common systems:
 UTM, Universal Transverse Mercator
 Public Land Survey System (PLSS) coordinates
 Latitude and Longitude (WGS84)
NSF DUE-1205110;
0903270
Public Survey
 Public Land Survey System (PLSS) used to survey most




of the Western US and Western Canada
Used to determine ownership
Doesn’t account for the curvature of the earth
Divides areas into townships, ranges, sections, and
quarter sections
Coordinate systems typically in meters or feet
NSF DUE-1205110;
0903270
Latitude and Longitude
 Geographic coordinates
 Starts at the equator and the prime meridian
 Units of measurement are degrees, minutes, and
seconds
 60 minutes in a degree
 60 seconds in a minute
NSF DUE-1205110;
0903270
Spatial Reference
 Coordinate system
 Datum
 Projection
NSF DUE-1205110;
0903270
What is a datum?
 Model of the shape of the earth’s surface
 The earth is not a perfect sphere
 Spheroid = equation attempting to model the actual
shape of the earth’s surface
Spheroid
Earth’s
Surface
Origins
NSF DUE-1205110;
0903270
What is a Datum?
 Datums define:
 shape of the earth
 location of latitude and longitude of origin
NSF DUE-1205110;
0903270
Datums
Earth’s Surface
Datum
NSF DUE-1205110;
0903270
Common Datums
 NAD27
 NAD83
 WGS84
 What do you think will happen if you use the wrong
datum?
NSF DUE-1205110;
0903270
Spatial Reference
 Coordinate system
 Datum
 Projection
NSF DUE-1205110;
0903270
Projections
 Take a 3-D world and make it 2-D
NSF DUE-1205110;
0903270
Projections
 Important to know what projection you are using to
minimize measurement and display errors
 Projections are a way of taking a 3-D object (earth) and
making a 2-D object (map)
NSF DUE-1205110;
0903270
Errors
 Projections usually try to hold one of the following
constant:
 Conformal (keep shapes the same)
 Equal area (keep areas the same)
 Equidistant (keep distances the same)
 No projection can achieve all three
 Some use a compromise of each
NSF DUE-1205110;
0903270
Projections
 Three ways of projecting
 Cylindrical
Earth
 Conic
 Planar
Earth
Earth
Wherever the
projection surface
“touches” the earth,
there will be the least
amount of distortion.
NSF DUE-1205110;
0903270
Common Spatial References
 Albers Equal-area
 Projection, good for large areas where area measures
are important
 Lambert conformal conic
 Also good for large areas where visualization is
important
NSF DUE-1205110;
0903270
Common Spatial References
 Universal Transverse Mercator (UTM)
 One of the most common coordinate systems and
projections
 Measures in meters
 Has “Zones”
 Great for local areas
 Geographic or Cylindrical Equidistant
 No projection or datum
 Just has coordinates assigned
 Directions true, All else distorted
NSF DUE-1205110;
0903270
Common Spatial References
 State Plane system
 Varies by state
 Specifies projection, coordinates, and datum
 Good for state-wide analyses
 Some states have multiple coordinate systems

For example, Texas
 Can use UTM, Lambert, Albers, or own projection
 Good for surveying
NSF DUE-1205110;
0903270
Questions?
Module name and number
NSF DUE-1205110;
0903270