Geographical concepts
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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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Geographical concepts

Geographical Concepts

IDigBio Train the Trainers Georeferencing WorkshopGainesville, Fl8-12, Oct 2012


Geographical concepts1

Geographical Concepts

  • 3 main concepts

    • Projection

    • Datum

    • Coordinate system


Geographical concepts projections

Geographical Concepts: Projections


Geographical concepts projections1

Geographical Concepts: Projections

Bonne equal-area projection


Geographical concepts projections2

Geographical Concepts: Projections


What projections do

What projections do

Rectangular projection

Tissot’sIndicatrix of distortion


Projections examples

ProjectionsExamples

Geographic

preserves NS distance

Mercator

preserves shape (terrible for poles, distorts area)


Geographical concepts

Projections: Take Home Message

  • Projections compromises…

    • Equal-area

    • True shape

    • True scale

    • True direction

  • Select projection to fit your needs


Geographical concepts datum

Geographical Concepts: Datum


Geographical concepts datums

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


Geographical concepts coordinate systems

Geographical Concepts: Coordinate Systems


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