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
Sphere Flat Map Map Projection
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.
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
Classification of Projections Cylindrical Projections Conical Projections Planar or Azimuthal Projections
Example – Cylindrical
Example – Conical
Example – Planar
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
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).
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
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
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
Mercator projection It preserves shapes (angles), i.e., it is a conformal projection . It distorts Areas Distances
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)
Lambert Conformal Conic projection
Equal-Area Projections Preserves Area (size) Equivalent or equal-area Represent the area of regions is correct or constant proportion to earth reality