3_map projection_map scale_coordinate system (3) - GEOG 563 GIS Map Projections Map Scale Geographic Coordinate Systems Sphere Flat Map Map Projection

3_map projection_map scale_coordinate system (3) - GEOG 563...

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GEOG 563: GIS Map Projections Map Scale Geographic Coordinate Systems
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Sphere Flat Map Map Projection
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Map Projections A projection is a mathematical means that transforms information from the Earth’s curved surface to a two- dimensional medium—paper or a computer screen Transforming a globe surface to a flat surface always results in distortion (e.g., area , distance , direction , and shape —ADDS) Move from 3D to 2D Cannot preserve all properties.
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Both areas and angles are distorted The simplest projection – “ Geographic Projection” - simply uses latitude and longitude as “2-D” coordinates (although they are actually defined on a 3D globe) Map Projections
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Classification of Projections Cylindrical Projections Conical Projections Planar or Azimuthal Projections
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Example – Cylindrical
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Example – Conical
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Example – Planar
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Classification of Map Projections Disposition of the projection plane Secant – cut through the earth Tangent – lie flat at a tangent to some point on the globe
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Standard Point/Line(s) Standard point Standard line(s) Standard parallels Measures are most accurate where the projection surface touches the sphere, i.e., at the standard line(s).
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Classification of Map Projections Aspect ( How the earth is viewed when it is projected ) Normal (Equatorial): standard point is on the equator or standard lines are parallels Transverse (Polar): standard point is on north/south pole or standard lines are parallel to meridians Oblique: none of the above
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Distortions in a map projection Areas If a projection preserves area, it is called an equal- area projections Shapes If a projection preserves shape (and thus angels), it is called conformal projections Distances If a projection preserves distance, it is called an equal-distance projection. Directions
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Conformal Map Projections Preserves Shape No projection can provide correct shapes for large areas Conformal projections - Show accurate shapes for small areas by preserving correct angular relationships (directions) Parallels and meridians intersect at right angles , as they do on the globe, but the size is distorted A map CANNOT be both equivalent and conformal. Examples: Mercator Lambert conformal conic
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Mercator projection It preserves shapes (angles), i.e., it is a conformal projection . It distorts Areas Distances
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Lambert Conformal Conic projection It preserves angles (you can simply tell from its name) It is used for mapping countries and regions of primarily east-west extent (such as the U.S. and Russia). It is also used as the basis of the U.S. State Plane Coordinate System (which you will learn later)
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Lambert Conformal Conic projection
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Equal-Area Projections Preserves Area (size) Equivalent or equal-area Represent the area of regions is correct or constant proportion to earth reality
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