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GTECH 361

GTECH 361. Lecture 04 Referencing Data to Real Locations. Today’s Content. Two types of coordinate systems Geographic Projected. Today’s Objectives. name two types of coordinate systems identify components of each type of coordinate system

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GTECH 361

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  1. GTECH 361 Lecture 04Referencing Data to Real Locations

  2. Today’s Content • Two types of coordinate systems • Geographic • Projected

  3. Today’s Objectives • name two types of coordinate systems • identify components of each type of coordinate system • assign coordinate system information to a dataset • set display units for a data frame and measure distances on a map • explain what a map projection is • list the major categories of map projections • list spatial properties that may be distorted when different map projections are applied • change the map projection for a data frame and describe its effects

  4. Geographic Coordinates • Graticule • Latitude • Longitude • Prime Meridian

  5. The Earth’s Shape • The ancient Greek’s mathematical harmony • Simplest approximation: the sphere

  6. The Earth as an Ellipsoid

  7. Making of an Ellipsoid

  8. The Earth’s Shape

  9. Why Multiple Datums?

  10. Geodetic Datums

  11. Projected Coordinates • Flattening the Earth

  12. Origin of X, Y Coordinates

  13. Central Parallel

  14. False Easting/northing

  15. Coordinates in ArcGIS • All geographic data have geographic coordinates (lat/lon) • Some may have projected coordinates in addition to the geographic ones • ArcGIS assigns the coordinate system to a map based on the GCS or PCS of the first dataset loaded • Subsequent datasets are converted on-the-fly

  16. Map and Display Units • Map units are determined by GCS or PCS • GCS in degrees or decimal degrees • PCS usually in feet or meters • Display units are determined by you • They are defined as part of the data frame

  17. (Decimal) Degrees • Converting from degrees to decimal degrees • Divide each value by the number of minutes (60) or seconds (3600) in a degree • Add up the degrees to get the answer

  18. Map Projection Types • Cylindrical • Planar • Conical

  19. Cylindrical Projections

  20. Conic Projections

  21. Planar Projections

  22. Understanding Distortion • Distortion cannot be avoided; we have to choose from distortion of • Shape • Area • Distance • Direction

  23. Preserving Properties • If two properties are to be preserved then one is always direction • These properties are incompatible:

  24. Shape Property • Conformal • Non-conformal

  25. Area Property

  26. Distance Property

  27. Direction Property

  28. Direction Property • Azimuthal map with shortest distance • Mercator with rhumb line or loxodrome

  29. Tissot Indicatrices

  30. Equatorial (normal) Aspect

  31. Transverse Aspect

  32. Oblique Aspect

  33. Aspects for Planar Projections • Polar Gnomic Stereographic Orthographic

  34. Aspects for Planar Projections • Equatorial Aspect Gnomic Stereographic Orthographic

  35. Aspects for Planar Projections • Oblique Aspect Gnomic Stereographic Orthographic

  36. Aspects for Conic Projections • Normal aspect

  37. Polyconic Projection • Hassler, 1820sUS Coastal Survey

  38. Perspective • Position of thelight source

  39. Perspectives

  40. Classifying Projections

  41. Classifying Projections

  42. Choosing a Map Projection • Conformal (shape-preserving) maps • Topographic and cadastral • Navigation • Civil engineering • Weather

  43. Choosing a Map Projection • Area-preserving maps • Population density • Land use • Quantitative attributes

  44. Choosing a Map Projection • Scale-preserving mapsno map preserves true distance for all measurements • Airline distances • Distance from epicenter of an earthquake • Cost calculations

  45. Choosing a Map Projection

  46. Components of a GCS • An angular unit of measure • A prime meridian • A datum, which includes a spheroid

  47. Planar Coordinate Systems

  48. Cartesian Coordinates • Calculate distance A-B

  49. Universal Transverse Mercator • UTM zones

  50. UTM Zones • .. as seen from the North Pole

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