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Geographical Concepts

Geographical Concepts. IDigBio Train the Trainers Georeferencing Workshop Gainesville, Fl 8-12, Oct 2012. Geographical Concepts. 3 main concepts Projection Datum Coordinate system. Geographical Concepts: Projections. Geographical Concepts : Projections. Bonne equal-area projection .

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Geographical Concepts

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  1. Geographical Concepts IDigBio Train the Trainers Georeferencing WorkshopGainesville, Fl8-12, Oct 2012

  2. Geographical Concepts • 3 main concepts • Projection • Datum • Coordinate system

  3. Geographical Concepts: Projections

  4. Geographical Concepts: Projections Bonne equal-area projection

  5. Geographical Concepts: Projections

  6. What projections do Rectangular projection Tissot’sIndicatrix of distortion

  7. ProjectionsExamples Geographic preserves NS distance Mercator preserves shape (terrible for poles, distorts area)

  8. Projections: Take Home Message • Projections compromises… • Equal-area • True shape • True scale • True direction • Select projection to fit your needs

  9. Geographical Concepts: Datum

  10. Geographical Concepts: Datums Common Datums NAD27 (North American Datum): system derived from land-based surveys, using Clarke 1886 ellipsoid NAD83: satellite-based system using the Earth’s center as a reference point; eventually adopted as GRS80 (Geodetic Ref. System 1980) WGS84 (World Geodetic System 1984): mathematically refined GRS80 used by the US military and default for GPS For most uses, NAD83, GRS80, WGS84 are equivalent

  11. Geographical Concepts: Coordinate Systems

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