Lecture 7- 2.12.docx - Map Projection Map Projection o Round Earth must be transformed to flat maps o Earth shape(geoid Flattened at the poles and

# Lecture 7- 2.12.docx - Map Projection Map Projection o...

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Map Projection Map Projection o Round Earth must be transformed to flat maps o Earth shape (geoid): Flattened at the poles and extended at the equator o Map Projection: is a method of representing the ellipsoidal (Earth) surface to a plane surface o Map projection process: Earth flat map o Selecting reference ellipsoid: geoid Reference ellipsoid o Selecting developable surface: reference ellipsoid developable surface o Transformation: Earth flat map, that is, a map projection is generated o Projection graticule: the projected meridians and parallels, are called the projection graticule. Map Projection o Three basic forms of developable surface: Cylinder Cone Plane o Leads to three families of map projections: Cylindrical Projection Conic Projection Planar or azimuthal projection Map Projection o Tangent: a line that touches a curved surface at a point o Secant: a line that intersects a circle at two points Plane or Azimuthal Projection o Projection aspect (The plane is tangent at the pole, mid-latitude, and equator and are called polar aspect, oblique aspect, and equatorial aspect, respectively) o 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 o Developed by wrapping a flat plane into a cylinder and making it tangent along a line or lines (secant) on the sphere o The tangent line is the equator o Area, angle, distance, or direction may be distorted o 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 o Developed by transferring points from globe grid to a cone enveloped around the sphere and this cone is then unrolled into a flat plane o