Map Projection
Map Projection
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Round Earth must be transformed to flat maps
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Earth shape (geoid): Flattened at the poles and extended at the equator
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Map Projection: is a method of representing the ellipsoidal (Earth) surface to a plane
surface
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Map projection process: Earth
flat map
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Selecting reference ellipsoid: geoid
Reference ellipsoid
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Selecting developable surface: reference ellipsoid
developable surface
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Transformation: Earth
flat map, that is, a map projection is generated
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Projection graticule: the projected meridians and parallels, are called the projection
graticule.
Map Projection
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Three basic forms of developable surface:
Cylinder
Cone
Plane
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Leads to three families of map projections:
Cylindrical Projection
Conic Projection
Planar or azimuthal projection
Map Projection
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Tangent: a line that touches a curved surface at a point
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Secant: a line that intersects a circle at two points
Plane or Azimuthal Projection
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Projection aspect (The plane is tangent at the pole, mid-latitude, and equator and are
called polar aspect, oblique aspect, and equatorial aspect, respectively)
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Directions from the projection’s center to all points are correct, and other directions are
not accurate. Distortion increases with distance from the tangent- standard point and
line
Cylindrical (or rectangular) Projection
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Developed by wrapping a flat plane into a cylinder and making it tangent along a line or
lines (secant) on the sphere
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The tangent line is the equator
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Area, angle, distance, or direction may be distorted
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Bands parallel to the line or lines of tangency are least distorted and increasing
exaggeration toward the outer edges of the map plane
Conic Projection
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Developed by transferring points from globe grid to a cone enveloped around the sphere
and this cone is then unrolled into a flat plane
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