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# Map projections

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### Map projections

1. 1. An important consideration in mapping our world Map Projections
2. 2. Map Projection  Transforming three- dimensional space onto a two dimensional map.  Define the spatial relationship between locations on Earth and their relative locations on a map.
3. 3. Why project data?  Data often comes in geographic, or spherical coordinates (latitude and longitude) and cannot be used for area calculations.  Some projections work better for different parts of the globe giving more accurate calculations.
4. 4. “All maps lie flat, therefore all maps lie.”
5. 5. Issues and Limitations Map projections are attempts to portray the surface of the Earth or a portion of the Earth on a flat surface. Some distortions of different types always result from this process. Some projections minimize distortions in some of these properties at the expense of maximizing errors in others. Some projections are attempts to only moderately distort all of these properties.
6. 6. Thus, the best projection depends upon the use of the map.
7. 7. Choosing a Map Projection depends on • which region to display (e.g. world, north pole, equator, US) • Resolution of the region • Geometric properties of the region • Purpose of using maps such that distortion can be minimized
8. 8. Distortion Types  Conformality When the scale of a map at any point is the same in any direction, the projection is conformal. Meridians (lines of longitude) and parallels (lines of latitude) intersect at right angles. Shape is preserved locally.  Distance A map is equidistant when its distance from a single location to all other locations are preserved.  Direction A map preserves directions when it is azimuthal, when direction from a single location to all other locations are preserved.
9. 9.  Scale It is the relationship between a distance portrayed on a map and the same distance on the Earth.  Area When a map portrays areas over the entire map so that all mapped areas have the same proportional relationship to the areas on the Earth that they represent, the map is an equal –area map.
10. 10. Aspects of the Projection  The aspect describes how the developable surface is placed relative to the globe. It may be; normal -such that the surface's axis of symmetry coincides with the Earth's axis transverse -at right angles to the Earth's axis or oblique -any angle in between • The developable surface may also be either; tangent -means the surface touches but does not slice through the globe; secant -means the surface does slice through the globe.
11. 11. Tangent Surface
12. 12. Secant surface
13. 13. Projection Types Projections can be conceptually created by projecting from one geometric shape (a sphere) onto another (a cone, cylinder, or plane).
14. 14. Cylindrical Projections  Good for displaying the world  Globe is projected onto a cylinder tangent at equator.  Low distortion at equator  Higher distortion approaching poles  A good choice for use in equatorial and tropical regions, e.g., Ecuador, Kenya, Malaysia
15. 15. Example of a Cylindrical Projection: Mercator  Invented by Gerhardus Mercator- Flemish Cartographer- in 1569  A special purpose projection, intended as a navigational tool  It is conformal, azimuthal, and has true scale around equator.
16. 16. Problems with Mercator  Preserves shape (a conformal type) but distorts area  Used by John Birch Society in Cold War to show “Red Menace”  Africa, in reality is 14X larger than Greenland in area.  Poles cannot be shown
17. 17. Conic Projections  Good for displaying mid- latitude area such as U.S.  Surface of globe projected onto cone is tangent at standard parallel.  Distorts N & S of standard parallel(s)  Normally shows just one semi hemisphere in middle latitudes.
18. 18. Conic Projection
19. 19.  Lambert Conformal Conic is a widely used example.
20. 20. Planar or Polar Projection  Good for displaying hemisphere with one focus.  Surface of globe is projected onto a plane tangent at only one point (frequently N or S pole).  Works well in highlighting an area.  Shows true bearing and distance to other points from center or point of tangency.
21. 21. Elliptical/Pseudocylindrical Projection  Also called “football” projection  Tend to be equal- area  Not bad for world maps Example: Mollweide Projection
22. 22. Goode’s Homosoline Interrupted Elliptical Projection  Equal-area  Good for climate, soils, landcover – latitude and area comparisons  Mild distortion of shapes  Interrupts areas- oceans, Greenland
23. 23. Thank you for listening! Credits to: Chelsea P. del Rosario Julian Philipp A. Soriano Shaina Mavreen Villaroza