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Working with georeferenced data

Working with georeferenced data. Lesson 8 overview. Georeferencing Coordinate systems Datums Projections and distortion Projecting your data. What is georeferencing?. Data is referenced to a location on the earth’s surface Geographic coordinate systems Projected coordinate systems. Y.

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Working with georeferenced data

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  1. Working with georeferenced data

  2. Lesson 8 overview • Georeferencing • Coordinate systems • Datums • Projections and distortion • Projecting your data

  3. What is georeferencing? • Data is referenced to a location on the earth’s surface • Geographic coordinate systems • Projected coordinate systems

  4. Y Data usually here - X + Y + X + Y X - X - Y + X - Y Coordinate systems • Geographic coordinate system • Latitude and longitude are not uniform across the earth’s surface • Cartesian coordinate system • Measures of length and angle are uniform

  5. Datums and datum conversion • A frame of reference for measuring locations on the surface of the earth • Measurements are referenced to a geodetic origin and an ellipsoid model Local datum NAD27 Ellipsoid CLARKE 1866 Earth-centered datum NAD83 Ellipsoid GRS80 Meades Ranch Kansas + + Earth’s surface Earth’s center

  6. Referencing locations • Locations on the earth are referenced to the datum • Different datums have different coordinate values for the same location I-10 through Redlands, CA UTM NAD83 UTM NAD27

  7. Map projections • Map projections convert curved surface to flat surface Cylinder Cone Plane

  8. Projection distortion • Distortions make geographers SADD 3D Earth 2D Map Shape Area Distance Direction

  9. Types of projections • Generally classified by the spatial attribute they preserve Projection type Maintains Example Conformal Shape Lambert Conformal Conic Equal area Area Albers Equal Area Conic Equidistant Distance Equidistant Conic Azimuthal Direction Lambert Equal Area Azimuthal

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