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10 Cards in this Set
- Front
- Back
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Projection - Definition
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Systematic construction of features on a plane surace to represent corresponding features on a spherical surface
Always results in distortions |
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Distortions - Tradeoffs
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Equal Area Projection: preserve AREA of features
Conformal Projections: Preserve SHAPE of small features, show directions correctly. Equidistant Projections: Preserve DISTANCES between 2 points |
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Distortion varies across map
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If flat surface "inside" ellipsoid surface, AB > ab
If flat surface "outside" ellipsoid surface, DE < de |
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Specifying Projections
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Type of developable surface (lambert conformal conic)
Size/shape of EARTH, size/shape of surface (geoid) Where surface intersects ellipsoid (upper and lower parallel) Location of map projection origin on the surface (lower parallel and central meridian) Coordinate system units |
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Projection Surfaces
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Cylindrical: produces 2D flat surface where circles of equal degree are ellipses along lines of longitude
Conic: produces a 2D flat surface where circles of equal degree are ellipses along lines of latitude |
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Defining "Standard" Projection
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Imposes uniformity
Facilitates data exchange Provides quality control Establishes limits on distortion |
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CA State Plane Coord System
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State partitioned into zones
Each has a different projection w/ distortion limit |
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Universal Transverse Mercator (UTM)
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World zonal numbering system
- Each zone 6 deg wide - Location defined by meridian - Coords discontinuous across zone boundaries NorCal in Zone 10 SoCal in Zone 11 |
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Control Points
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Exact positions of often-surveyed geographic features used to register map sheets and transform coordinates.
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Transforming is an ___ process
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Iterative
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