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