Geographic Projections and Coordinate Systems

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Geographic Projections and Coordinate Systems
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What are projections?

• Projections are a means of representing a round
  object on flat paper
• DISTORTION!!!!
• Equal area vs. Equal distance
• Spheroids A model of the earth
• Datum a reference point
• Projections are often designed to represent a
  portion of the earth.

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What are coordinate systems?

• All data contains coordinates
• Ex. Lat/Lon
• Coordinates start from an origin
• What is the Lat/Lon origin?
• Projected coordinates are scaled (in meters,
  feet, etc.)
• Coordinates are used by GIS to display the data.

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Common Projections

• UTM Universal Transverse Mercator
• In zones with a specific lat/lon origin.
• State Plane
• Used by states.
• Contains zones (like UTM)
• Based on NAD 27 or NAD 83
• Albers California

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Data Sources

• California Albers
• NRCS DD
• County Data State Plane
• GPS Data DD or UTM
• Ortho-photos UTM

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Data on the Web

• http//www.esri.com
• http//www.ftw.nrcs.usda.gov/ssur_data.html
• http//www.gis.ca.gov
• http//terraserver.homeadvisor.msn.com/

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Demonstration

• ArcView Projection Wizard