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24 Cards in this Set
- Front
- Back
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Map - Definition
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"Representation, normally to scale and on a flat medium, of a selection of material or abstract features on or in relation to, surface of Earth
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Map - Paradigm Shift in Cartography
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From communication to analytical paradigm
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Map - Elements
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Theme
Legend Projection Scale "Metadata" |
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Theme (ArcView) = Coverage (ArcInfo) = Layer (ArcMap)
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Thematic map displays locations of a single attribute or relationships among several selected attributes
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Legend
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Explains colors, symbols, line patterns, shadings, scale, etc.
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Map Registration is a Statistical Process
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Coordinate ERROR
Pointing ERROR Media DISTORTIONS Systematic ERROR |
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Geodesy
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Science that deals with the measurement of the curvature, shape, and dimensions of Earth
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DATUM
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Collectively, the reference points used to prepare a map
A smooth mathematical reference surface that closely fits mean sea-level surface throughout area of interest |
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Site Datum
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Reference height against which elevations are measured
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Earth-centered datums
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Cover the globe in one coordinate system with center of the Earth as the origin
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Building a Datum - Technologies
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Traingulation Network (consisting of survey stations, survey legs, etc.)
Astronomical observation Initial, intermittent, and ending baselines Multiple, redundant angle measurements |
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Triangulation
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Basic Trigonometry:
If you know length of A and angles a, b, and c, can calculate lengths of B and C. |
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Earth as an Ellipsoid (1670)
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Newton: earth would be flattened at the poles (centrifugal force)
Semi-major axis thru equator Semi-minor axis thru poles |
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Earth not as an Ellipsoid
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Measured by French expeditions at widely separate latitudes
Deviations from ellipsoid due to difference in gravitational pull of earth (not the surface topography) |
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Earth as a Geoid
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Measured surface (w/ gravimeters)
Approximation of mean sea level Direction of gravity is perpendicular to geoid |
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Average separation between Geoid and best-fitting ellipsoid
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30 meters
(Undulation always below 100m) |
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Different Ellipsoids in Different Countries
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There are locally "best fit" ellipsoides
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Latitude/Longitude defined by
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Spheroid (specified ellipsoid)
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Orthometric Heights
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Specified relative to Geoid (Conventional)
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Spheroidal Heights
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Heights above the ellipsoid (usually used to specify geoid-ellipsoid separation)
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Public Land Survey System
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The non-coordinate system
Method of defining parcels by successive subdivision (think of historical townships) |
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Metes and Bounds
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escription of a tract of land by starting at a given point, running so many feet a certain direction, so many feet another direction etc., back to the point of beginning.
Descriptions have: point of beginning, definite corners, lengths and directions of property sides, names of adjoining property owners and area. Use for land titles and transactions (esp. in Eastern states) |
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Scale
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Ration between distances on the map and corresponding didstances in real world
Small scale (1: 500,000) "great surfaces" Large Scale (1:500) "great detail" |
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Metadata "data about data"
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Describes overall theme, quality, source, spatial reference, etc.
"data dictionary" defines attributes and relationships |
