1. Lecture 04 Referencing Data to Real Locations
GTECH 361
Lecture 04 Referencing 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
Conical
Planar

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 Mercator with rhumb line or loxodrome
Azimuthal map with shortest distance

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, 1820s US Coastal Survey

38. Perspective
Position of the light source

39. Perspectives

40. Classifying Projections

41. Classifying Projections
Cylindrical
straight parallels; straight meridians
Pseudo-cylindrical
straight parallels, curved meridians
Conic
partial concentric circles for parallels; straight meridians
Pseudo-conic
partial concentric circles for parallels; curved meridians
Planar
Concentric circles for parallels; straight meridians
Modified planar
No common appearance of parallels and meridians

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 maps no 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

51. UTM Projections
Each zone uses a custom Transverse Mercator projection with its own central meridian

52. Universal Polar Stereographic
Fills the holes of UTM in polar regions

53. State Plane Coordinate System

54. SPC N-S zones use Transverse Mercator
E-W zones use Lambert Conformal Conic
Maximal scale error is 1:10,000
NAD27 or NAD83 datum

55. Public Land Survey System
PLS are shown in purple

56. PLS It is used to locate areas, not points
It is not rigorous enough for spatial analysis like the calculation of distance or direction
It is not a grid imposed on a map projection (a system invented in a room), but lines measured on the ground by surveyors

57. PLS Meridians and Baselines

58. PLS Area Unit Hierarchy

59. PLS Township Sections
A township is divided into 36 sections, each a square mile (640 acres)
A section is divided into 160-acre quarters, which can be further divided into halves, quarters, and so on