geographical concepts
DESCRIPTION
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 . - PowerPoint PPT PresentationTRANSCRIPT
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Geographical Concepts
IDigBio Train the Trainers Georeferencing WorkshopGainesville, Fl 8-12, Oct 2012
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• 3 main concepts– Projection– Datum– Coordinate system
Geographical Concepts
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Geographical Concepts: Projections
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Geographical Concepts: Projections
Bonne equal-area projection
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Geographical Concepts: Projections
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What projections do
Tissot’s Indicatrix of distortion
Rectangular projection
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Projections Examples
Geographicpreserves NS distance
Mercatorpreserves shape (terrible for
poles, distorts area)
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• Projections compromises…– Equal-area– True shape– True scale– True direction
• Select projection to fit your needs
Projections: Take Home Message
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Geographical Concepts: Datum
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Common DatumsNAD27 (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
Geographical Concepts: Datums
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Geographical Concepts: Coordinate Systems