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GEOG 563: GISMap ProjectionsMap ScaleGeographic Coordinate Systems
SphereFlat MapMap Projection
Map ProjectionsA projection is a mathematical meansthat transforms information from the Earth’s curved surface to a two-dimensional medium—paper or a computer screenTransforming a globe surface to a flat surface always results in distortion (e.g., area, distance, direction, and shape—ADDS)Move from 3D to 2DCannot preserve all properties.
Both areas and angles are distortedThe 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 ProjectionsCylindrical ProjectionsConical ProjectionsPlanar or Azimuthal Projections
Example – Cylindrical
Example – Conical
Example – Planar
Classification of Map ProjectionsDisposition of the projection planeSecant– cut through the earth Tangent– lie flat at a tangent to some point on the globe
Standard Point/Line(s)Standard pointStandard line(s)Standard parallelsMeasures are most accurate where the projection surfacetouches the sphere, i.e., at the standard line(s).
Classification of Map ProjectionsAspect(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 projectionAreasIf a projection preserves area, it is called an equal-area projections ShapesIf a projection preserves shape (and thus angels), it is called conformal projectionsDistancesIf a projection preserves distance, it is called an equal-distance projection. Directions
Conformal Map ProjectionsPreserves ShapeNo projection can provide correct shapes for large areasConformal projections - Show accurate shapes for small areasby preserving correct angular relationships (directions)Parallels and meridians intersect at right angles, as they do on the globe, but the size is distortedA map CANNOT be both equivalent and conformal.Examples: MercatorLambert conformal conic
Mercator projectionIt preserves shapes (angles), i.e., it is a conformal projection.It distorts Areas Distances…
Lambert Conformal Conic projectionIt 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 ProjectionsPreserves Area (size)Equivalent or equal-areaRepresent the area of regions is correct or constant proportion to earth reality