1. Introduction to Geographic Information Systems Spring 2013 (INF 385T-28437) Dr. David Arctur Lecturer, Research Fellow University of Texas at Austin Lecture 5 February 7, 2013 Spatial Reference Systems, Data Sources

2. Outline  Models of the Earth  Map projections  Coordinate systems  GIS data sources  Vector data formats  Raster data formats 2 INF385T(28437) – Spring 2013 – Lecture 5

3. Models of the Earth’s shape  Sphere with radius of ~6378 km  Ellipsoid (or Spheroid) with equatorial radius (semimajor axis) of ~6378 km and polar radius (semiminor axis) of ~6357 km  Difference of ~21km usually expressed as “flattening” (f) ratio of the ellipsoid:  f = difference / major axis = ~ 1/300 for Earth  and “inverse flattening” would be ~300 3 INF385T(28437) – Spring 2013 – Lecture 5

4. Ellipsoid dimensions and flattening 4 INF385T(28437) – Spring 2013 – Lecture 5 Ellipsoid = Spheroid in GIS…

5. Ellipsoid vs Geoid vs Datum  The Geoid is approximately where sea level would be throughout the world (measured by plumb bob away from coastal areas)  Due to variations in the Earth’s gravity field, this “global sea level” would not fit any one ellipsoid, as evident in figure   Datum = shape of ellipsoid AND location of origin for axis of rotation relative to Earth center of mass

6. Horizontal Control Datums Commons North American Datums  NAD27 (1927 North American Datum)  Clarke (1866) ellipsoid, non-geocentric (local origin) for axis of rotation  NAD83 (1983 North American Datum)  GRS80 ellipsoid, geocentric origin for axis of rotation  WGS84 (1984 World Geodetic System)  WGS84 ellipsoid, geocentric, nearly identical to NAD83  Other datums are also in use globally 6 INF385T(28437) – Spring 2013 – Lecture 5

7. Datum shifts 7 INF385T(28437) – Spring 2013 – Lecture 5

8. Datum transformations  Theoretical method: use equations relating Lat/Lon in one datum to another  Empirical method: use grid of differences to convert values directly from one datum to another See Esri digital book on Map Projections for more information 8 INF385T(28437) – Spring 2013 – Lecture 5

9. MAP PROJECTIONS How do we get from 3D Earth to 2D maps??? 9 INF385T(28437) – Spring 2013 – Lecture 5

10. Latitude and longitude  Longitude (meridians) 10 INF385T(28437) – Spring 2013 – Lecture 5

11. Latitude and longitude  Latitude (parallels) 11 INF385T(28437) – Spring 2013 – Lecture 5

12. Latitude and longitude ° Longitude (prime meridian) 0 ° Latitude (equator) 0 12 INF385T(28437) – Spring 2013 – Lecture 5

13. Latitude and longitude Pittsburgh, PA USA -80 40  Coordinates 13 INF385T(28437) – Spring 2013 – Lecture 5

14. Lat/Long coordinates  Degrees, minutes, and seconds (DMS):  40° 26′ 2″ N latitude  -80° 0′ 58″ W longitude  Decimal degrees (DD)  1 degree = 60 minutes,  1 minute = 60 seconds  40° 26′ 2″ =  40 + 26/60 + 2/3600 =  40 +.43333 +.00055 =  40.434° 14 INF385T(28437) – Spring 2013 – Lecture 5

15. Lat/long coordinates Translated to distance  World circumference through the poles is 24,859.82 miles, so for latitude:  1° = 24,859.82 / 360 = 69.1 miles  1′ = 24,859.82 / (360 * 60) = 1.15 miles  1″ = 24,859.82 * 5,280 / (360 * 3,600) = 101 feet  Length of the equator is 24,901.55 miles 15 INF385T(28437) – Spring 2013 – Lecture 5

16. Picking a projection … [or: how big do you like Greenland?] 16 INF385T(28437) – Spring 2013 – Lecture 5

17. Most-used methods 17 INF385T(28437) – Spring 2013 – Lecture 5

18. Still more distinctions among projections 18 INF385T(28437) – Spring 2013 – Lecture 5

19. Mercator projection (1569)  Conformal projection  Cylindrical  Parallels and meridians at right angles  Linear scale is constant in all directions around any point  Preserves angles and shapes of small objects  Distorts the size and shape of large objects  Map projection for nautical purposes 19 INF385T(28437) – Spring 2013 – Lecture 5

20. 20 INF385T(28437) – Spring 2013 – Lecture 5

21. Hammer – Aitoff (1882-1889)  Equal-area  Modified azimuthal projection  Good for population density (world area)  Difficult to see some areas 21 INF385T(28437) – Spring 2013 – Lecture 5

22. Robinson projection (1961)  Pseudocylindrical  Neither equal area nor conformal  Meridians curve gently, avoiding extremes  Good compromise projection for viewing entire world  Used by Rand McNally since the 1960s and by the National Geographic Society (1988 and 1998) 22 INF385T(28437) – Spring 2013 – Lecture 5

23. 23 INF385T(28437) – Spring 2013 – Lecture 5

24. Albers Equal Area  Conic projection  Scale and shape are not preserved, distortion is minimal between the standard parallels  Standard projection for British Columbia, U.S. Geological Survey, U.S. Census Bureau 24 INF385T(28437) – Spring 2013 – Lecture 5

25. Other map projections… 25 INF385T(28437) – Spring 2013 – Lecture 5 http://xkcd.com/977/ http://www.watermanpolyhedron.com/maps

26. And the ever-popular… 26 INF385T(28437) – Spring 2013 – Lecture 5 Bovine projection(s) Spilled Coffee Projection

27. Projection important for…  Measurements used to make important decisions  Comparing shapes, areas, distances, or directions of map features  Feature and image themes are aligned Los Angeles New York Los Angeles New York Projection: Mercator Distance: 3,124.67 miles Projection: Albers equal area Distance: 2,455.03 miles Actual distance: 2,451 miles 27 INF385T(28437) – Spring 2013 – Lecture 5

28. Projection not important for…  Business applications  Not of critical importance  Concerned with the relative location of different features  Large scale maps — street maps  Distortion may be negligible  Map covers only a small part of the earth’s surface 28 INF385T(28437) – Spring 2013 – Lecture 5

29. COORDINATE SYSTEMS Lecture 5 29 INF385T(28437) – Spring 2013 – Lecture 5

30. Geographic Coordinate System (GCS)  Spherical coordinates  Angles of rotation of a radius anchored at earth’s center  Latitude and longitude  Census Bureau TIGER files 30 INF385T(28437) – Spring 2013 – Lecture 5

31. U.S. Census GCS example 31 INF385T(28437) – Spring 2013 – Lecture 5

32. Rectangular coordinate system  Used for locating an intersection on a flat sheet of graph paper or a flat map  Cartesian coordinates (x,y)  State plane and UTM 32 INF385T(28437) – Spring 2013 – Lecture 5

33. State Plane coordinates  Established by the U.S. Coast and Geodetic Survey in 1930s  Originally North American Datum (NAD 1927)  More recently NAD 1983 and 1983 HARN  Used by local U.S. governments  All positive coordinates in feet (or meters) 33 INF385T(28437) – Spring 2013 – Lecture 5

34. State Plane zones  125 zones  At least one for each state  Cannot have zones joined to make larger regions  Follow state and county boundaries  Each has its own projection:  Lambert conformal projection for zones with east-west extent  Transverse Mercator projection for zones with north-south extent 34 INF385T(28437) – Spring 2013 – Lecture 5

35. State Plane zones 35 INF385T(28437) – Spring 2013 – Lecture 5

36. State Plane zones 36 INF385T(28437) – Spring 2013 – Lecture 5

37. Pittsburgh neighborhoods as state plane coordinates 37 INF385T(28437) – Spring 2013 – Lecture 5

38. Universal Transverse Mercator (UTM)  Rectangular coordinate system  Used by U.S. military  Covers entire world  Metric coordinates  Longitude zones are 6° wide  Latitude zones are 8° high 38 INF385T(28437) – Spring 2013 – Lecture 5

39. Coordinate system summary  Geographic coordinate system  U.S. Census  State plane coordinate system  Local governments  U.S. military  Projections defined in ArcCatalog or ArcMap (.prj) files  First file added in a map document sets the projection (others will adjust to it as long as they have a.prj file) 39 INF385T(28437) – Spring 2013 – Lecture 5

40. GIS DATA SOURCES We had to go through all that, so we can understand issues around importing spatial data from… 40 INF385T(28437) – Spring 2013 – Lecture 5

41. GIS data sources  ESRI  U.S. Census  USGS and other government sources  GDT Dynamap/2000 U.S. Street Data  Engineering companies  land surveys, aerial photos, CAD drawings  University Web sites (e.g. Penn State’s PASDA)  Zillions of others… 41 INF385T(28437) – Spring 2013 – Lecture 5

42. GIS data sources  30+ million Internet search results  type “GIS data download” or “population China.e00  add the name of the state, county, or city to the search 42 INF385T(28437) – Spring 2013 – Lecture 5

43. GIS departments Web sites  Washington, D.C.  dcgis.dc.gov/  Chicago, IL  www.cityofchicago.org/gis  Austin, TX  Tip: Search by county name (Travis County, Texas)  http://www.austintexas.gov/development/  ftp://ftp.ci.austin.tx.us/GIS-Data/Regional/coa_gis.html 43 INF385T(28437) – Spring 2013 – Lecture 5

44. ESRI’s Web site  http://www.esri.com/data/esri_data/demographic-overview http://www.esri.com/data/esri_data/demographic-overview 44 INF385T(28437) – Spring 2013 – Lecture 5

45. U.S. Census Bureau  Started building a map infrastructure in the late 1970s and early 1980s  Census mapping needs were twofold:  To assign census employees to areas of responsibility, covering the entire country and its possessions  To report and display census tabulations by area, officials determined that the smallest area needed for these purposes is a city block or its equivalent 45 INF385T(28437) – Spring 2013 – Lecture 5

46. U.S. Census Bureau  Compiles all line features used to create a block layer for the entire country  Map features smaller than are the responsibility of local governments  deeded land parcels  buildings  street curbs  parking lots  others? 46 INF385T(28437) – Spring 2013 – Lecture 5

47. Census TIGER/Line files  Topologically Integrated Geographic Encoding and Referencing files  Census Bureau’s product for digital mapping of the U.S.  Available for the entire U.S. and its possessions  Include the following geographic features  roads and street centerlines  railroads  rivers  lakes  census statistical boundaries 47 INF385T(28437) – Spring 2013 – Lecture 5

48. TIGER census tracts  Statistical boundary (below county level)  between 1,000 and 8,000 people (in general)  1,700 housing units or 4,000 people  homogeneous population characteristics (economic status and living conditions)  normally follow visible features  may follow governmental unit boundaries and other nonvisible features  more than 60,000 census tracts in Census 2000  Also, the legal basis for developing congressional districts 48 INF385T(28437) – Spring 2013 – Lecture 5

49. PA tracts 49 INF385T(28437) – Spring 2013 – Lecture 5

50. Allegheny County tracts 50 INF385T(28437) – Spring 2013 – Lecture 5

51. Pittsburgh tracts 51 INF385T(28437) – Spring 2013 – Lecture 5

52. TIGER census block groups  Subdivision of a census tract  400 housing units, with a minimum of 250 and a maximum of 550 housing units  Follow clearly visible features such as roads, rivers, and railroads 52 INF385T(28437) – Spring 2013 – Lecture 5

53. Census block groups 53 GIS TUTORIAL 1 - Basic Workbook

54. TIGER census blocks  Smallest geographic area for which the Census Bureau collects and tabulates decennial census information  Visible boundaries  street  road  stream  Shoreline  Nonvisible boundaries  county, city, neighborhood boundary  property line 54 GIS TUTORIAL 1 - Basic Workbook INF385T(28437) – Spring 2013 – Lecture 5 54

55. Census blocks 55 GIS TUTORIAL 1 - Basic Workbook

56. Other TIGER layers 56 INF385T(28437) – Spring 2013 – Lecture 5

57. U.S. Census Bureau data tables  http://factfinder2.census.gov/ http://factfinder2.census.gov/ 57 INF385T(28437) – Spring 2013 – Lecture 5

58. Summary File (SF1) tables 58 GIS TUTORIAL 1 - Basic Workbook

59. Summary File (SF3) tables 59 INF385T(28437) – Spring 2013 – Lecture 5

60. SF tables comparisons SF1  Population  Age  Sex  Race  Housing units  FFH SF3  Income  Educational attainment  Citizenship  Transportation  Detailed housing 60 INF385T(28437) – Spring 2013 – Lecture 5

61. Census summary  Shapefiles downloaded from www.census.gov or www.esri.com  Data tables downloaded from American Factfinder http://factfinder2.census.gov  Data joins needed to join SF1 or SF3 to shapefiles INF385T(28437) – Spring 2013 – Lecture 5 61

62. VECTOR DATA FORMATS Lecture 5 62 INF385T(28437) – Spring 2013 – Lecture 5

63. ArcInfo coverages  Created using ESRI’s ArcInfo software  Older format (import/export as “.e00”)  Set of files within a folder or directory called a workspace  Files represent different types of topology or feature types 63 INF385T(28437) – Spring 2013 – Lecture 5

64. Coverage attribute table  Area and perimeter  Coverage_ and Coverage_ID 64 INF385T(28437) – Spring 2013 – Lecture 5

65. Shapefiles  ArcView native format  Minimum files .shp–stores feature geometry .shx–stores index of features .dbf–stores attribute data  Additional files .prj–projection data .xml–metadata .sbn and.sbx–store additional indices 65 INF385T(28437) – Spring 2013 – Lecture 5

66. CAD drawings  CAD software  Autodesk, AutoCAD (.dwg)  Bentley, Microstation (.dgn,.dxf)  Often used by engineering companies  Architectural details, instructions to builders  Roads, bridges, dams  Better digitizing precision 66 INF385T(28437) – Spring 2013 – Lecture 5

67. CAD drawings 67 INF385T(28437) – Spring 2013 – Lecture 5

68. CAD layers 68 INF385T(28437) – Spring 2013 – Lecture 5

69. Event files Data table that includes map coordinates, such as latitude and longitude or projected coordinates 69 INF385T(28437) – Spring 2013 – Lecture 5

70. Event files 70 INF385T(28437) – Spring 2013 – Lecture 5

71. Export event files 71 INF385T(28437) – Spring 2013 – Lecture 5  Creates point features

72. RASTER DATA FORMATS Lecture 5 72 INF385T(28437) – Spring 2013 – Lecture 5

73. Digital file formats  TIFF (Tagged Image File Format) .tif file extension  Very high quality images  Commonly used in publishing  Sizes are large because it is uncompressed  GIF (Graphic Interchange Format): .gif as its file extension.  Ideal for schematic drawings that have relatively large areas with solid color fill and few color variations.  Small file sizes 73 INF385T(28437) – Spring 2013 – Lecture 5

74. Digital file formats  JPEG (Joint Photographic Experts Group): .jpg file extension.  Most widely used format for photographs and other images that have a lot of color variations  Uses file compression at the expense of picture detail, if you specify a lot of compression 74 INF385T(28437) – Spring 2013 – Lecture 5

75. Summary  Models of the Earth  Map projections  Coordinate systems  GIS data sources  Vector data formats  Raster data formats 75 INF385T(28437) – Spring 2013 – Lecture 5