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Representing Geography

Representing Geography. Datum. Defines the size, shape, and orientation of Earth Provides.. Origin: starting place that allows coordinates to be meaningful Clearly defined surface that the coordinate system is applied to. No datum = playing checkers without a checkerboard

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Representing Geography

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  1. Representing Geography

  2. Datum • Defines the size, shape, and orientation of Earth • Provides.. • Origin: starting place that allows coordinates to be meaningful • Clearly defined surface that the coordinate system is applied to. • No datum = playing checkers without a checkerboard • Defined by an ellipsoid model

  3. X Ellipsoid Models • Provide a reference for the datum and contribute to thedatum’s definition • Requires survey • measurements to define the shape ofthe earth • Clarke 1866 Ellipsoidbecame the standardreference model forNAD27 • Geodetic ReferenceSystem of 1980 is thefigure for NAD83

  4. Datum Realization • Creation of the physical network ofreference points on Earth • NGS established network of bronzedisks

  5. Datum Error • Errorless in abstract(when not connected to reality) • no distortion • every point has a unique and accurate coordinate • Error introduced when applied to reality • cannot measure perfectly from origin • ambiguity of finding center of objects

  6. NAD83 • Improved based on survey accuracy advances • GPS • Remote Sensing

  7. Coordinate Systems • Where are we? • 8800 Grossmont College Drive, El Cajon, CA 92020 • Building 30, Room 252 • 32° 49’ 00.7”N Latitude 117° 00’ 27”W Longitude • UTM, Zone 11, 0499297 Easting 3630983 Northing

  8. Coordinate Systems • Cartesian Coordinates • Rene Descartes (latin: RenatusCartesius) • first used graphs to plot/analyze math functions • setup rules for 2-D coordinate system • Basis for UTM system, State Plane • Geographic Grid • Spherical Grid System (illustrations)

  9. Data Representation • All spatial data converted to digital form is represented as… • Points • Lines • Areas (polygons) • Discrete Objectsvs Continuous Fields

  10. Classification of Data

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