1. Introduction to Geographic Information Systems Fall 2013 (INF 385T-28620) Spatial Reference Systems, Data Sources Dr. David Arctur Research Fellow, Adjunct Faculty University of Texas at Austin Lecture 5 September 19, 2013

2. Outline  Models of the Earth  Map coordinates  Map projections  US Census geographic files  US Census data files  Geospatial data sources 2 INF385T(28620) – Fall 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(28620) – Fall 2013 – Lecture 5

4. Ellipsoid dimensions and flattening 4 INF385T(28620) – Fall 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 INF385T(28620) – Fall 2013 – Lecture 5 5

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(28620) – Fall 2013 – Lecture 5

7. Datum shifts 7 INF385T(28620) – Fall 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(28620) – Fall 2013 – Lecture 5

9. MAP PROJECTIONS How do we get from 3D Earth to 2D maps???

10. Map projections  Way to represent the curved surface of the earth on the flat surface of a map  Hundreds of map projections  Each map projection has advantages and disadvantages:  Depends on the scale of the map  Depends on map’s purpose  Different projections good for small areas, areas with a large east–west extent, or areas with a large north–south extent 10 INF385T(28620) – Fall 2013 – Lecture 5

11. Picking a projection … [or: how big do you like Greenland?] 11 INF385T(28620) – Fall 2013 – Lecture 5

12. Map projections Flatten half of a rubber ball? No. Instead, features are projected onto one of three “developable” surfaces. http://www.nationalatlas.gov/articles/mapping/a_projections.html#two Conic: a map projection where the earth’s surface is projected onto a tangent or secant cone, which is then cut from apex to base and laid flat Cylindrical: a map projection where the earth’s surface is projected onto a tangent or secant cylinder, which is then cut lengthwise and laid flat Planar: a map projection resulting from the conceptual projection of the earth onto a tangent or secant plane 12 INF385T(28620) – Fall 2013 – Lecture 5

13. Most-used methods 13 INF385T(28620) – Fall 2013 – Lecture 5

14. Conformal projection  Cylindrical projection  Parallels and meridians at right angles  Angles and shapes of small objects preserved (at every point, east–west scale same as north–south scale)  The size/shape/area of large objects distorted (scale approaches infinity at the poles)  Seldom used for world maps Example: Mercator projection (1569) used for nautical purposes (constant courses are straight lines) 14 INF385T(28620) – Fall 2013 – Lecture 5

15. Equivalent projection  Conic projection  Preserves accurate area  Scale and shape are not preserved Example: Albers Equal Area standard projection for US Geological Survey, US Census Bureau 15 INF385T(28620) – Fall 2013 – Lecture 5

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18. Compromise projections  Neither equivalent nor conformal  Meridians curve gently, avoiding extremes.  Doesn’t preserve properties, but “looks right” Example: Robinson projection (1961) good compromise projection for viewing entire world used by Rand McNally and the National Geographic Society 18 INF385T(28620) – Fall 2013 – Lecture 5 18

19. And the ever-popular… 19 INF385T(28620) – Fall 2013 – Lecture 5 Bovine projection(s) Spilled Coffee Projection

20.  Small-scale maps  Comparing shapes, areas, distances, or directions of map features  Natural appearance desired New York Los Angeles When projection is important Los Angeles Projection: Mercator Distance: 3,124.67 miles Projection: Albers Equal Area Distance: 2,455.03 miles Actual distance: 2,451 miles Los Angeles 20 INF385T(28620) – Fall 2013 – Lecture 5 20

21. When projection is not important  Many business, policy, and management applications  On large-scale maps  Error is negligible 21 INF385T(28620) – Fall 2013 – Lecture 5 21

22. MAP COORDINATES Now here, know where, or nowhere?

23. Latitude and longitude ° longitude (prime meridian) 0 ° latitude (equator) 0 23 INF385T(28620) – Fall 2013 – Lecture 5

24. Latitude and longitude Pittsburgh, PA USA -80 40  Coordinates 24 INF385T(28620) – Fall 2013 – Lecture 5

25. 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° 25 INF385T(28620) – Fall 2013 – Lecture 5

26. Lat/long coordinates  Translated to distance  World circumference through the poles is 24,859.82 mi, so for latitude:  1° = 24,859.82 / 360 = 69.1 mi  1′ = 24,859.82 / (360 * 60) = 1.15 mi  1″ = 24,859.82 * 5,280 / (360 * 3,600) = 101 ft  Length of the equator is 24,901.55 mi 26 INF385T(28620) – Fall 2013 – Lecture 5

27. GCS example (census tracts) 27 INF385T(28620) – Fall 2013 – Lecture 5

28. Rectangular coordinates  UTM (universal transverse Mercator)  US military  State plane  Local US governments 28 INF385T(28620) – Fall 2013 – Lecture 5

29. UTM coordinates example  Developed by US Army Corps of Engineers (1940s)  Covers world, 80°S to 80°N  Metric coordinates  60 tuned transverse Mercator projections for longitude zones, 6° wide 29 INF385T(28620) – Fall 2013 – Lecture 5

30. State plane coordinates  Established by the US Coast and Geodetic Survey in the 1930s  All positive coordinates in feet or meters  Used by local US governments  Originally North American Datum (NAD 1927)  More recently NAD 1983 and 1983 HARN (High Accuracy Reference Network) 30 INF385T(28620) – Fall 2013 – Lecture 5

31. State plane zones  125 zones  At least one for each state  Cannot join zones to make larger regions  Follow state and county boundaries  Each zone has its own tuned projection  Lambert conformal projection for zones with east  west orientation  Transverse Mercator projection for zones with north  south orientation 31 INF385T(28620) – Fall 2013 – Lecture 5

32. State plane zones 32 INF385T(28620) – Fall 2013 – Lecture 5

33. State plane coordinates example  State plane NAD 1983, Pennsylvania South, Feet 33 INF385T(28620) – Fall 2013 – Lecture 5

34. X,Y coordinate tips  Always assign coordinates according to the agency US Census Geographic coordinate system (GCS) City of Pittsburgh State plane coordinate system 34 INF385T(28620) – Fall 2013 – Lecture 5

35. X,Y coordinate examples 35 US Census Geographic coordinates (GCS) Block groups City of Pittsburgh State plane coordinates Sidewalks 35 INF385T(28620) – Fall 2013 – Lecture 5

36. Map document tip  The first layer added in ArcMap sets the x,y coordinate system for the data frame  Additional layers will overlay properly as long as the correct coordinate system is assigned to feature class  For example, GCS to US Census files, state plane to local government files  Known as.prj files 36 INF385T(28620) – Fall 2013 – Lecture 5

37. Map document tip  Example: Sidewalks added first (state plane), but block groups match even though they are in geographic coordinate system (GCS) projection. 37 INF385T(28620) – Fall 2013 – Lecture 5

38. US CENSUS GEOGRAPHIC FILES Lecture 5

39. Census TIGER/Line files  http://www.census.gov/geo/www/tiger/ http://www.census.gov/geo/www/tiger/  Topologically Integrated Geographic Encoding and Referencing files  US Census Bureau product for digital mapping of the United States  TIGER maps available for the entire United States and its possessions, including roads and streets, railroads, rivers, lakes, political boundaries, and census statistical boundaries 39 INF385T(28620) – Fall 2013 – Lecture 5 39

40. Example census geographies 40 INF385T(28620) – Fall 2013 – Lecture 5 40

41. TIGER census tracts  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 invisible features 41 INF385T(28620) – Fall 2013 – Lecture 5

42. State tracts (2010) 42 INF385T(28620) – Fall 2013 – Lecture 5

43. County tracts (2000 and 2010) 43 INF385T(28620) – Fall 2013 – Lecture 5

44. City tracts (2000 and 2010) 44 INF385T(28620) – Fall 2013 – Lecture 5

45. City block groups (2000 and 2010)  Subdivisions of a census tract  400 housing units, with a min. of 250 and a max. of 550  Follow clearly visible features (roads, rivers, and railroads) 45 INF385T(28620) – Fall 2013 – Lecture 5

46. Census blocks  Smallest geographic areas for which the Census Bureau collects and tabulates decennial census information  Block boundaries visible (street, road, stream, shoreline, etc.) or invisible (county line, city limit, property line, etc.) 46 INF385T(28620) – Fall 2013 – Lecture 5

47. US CENSUS DATA FILES Lecture 5

48. Decennial census data  Years 2000 and 2010  Summary File 1 (SF 1)  Short form, entire population  Population  Age  Sex  Race  Families  Households  Housing units  Tracts, block groups, blocks 48 INF385T(28620) – Fall 2013 – Lecture 5

49. Decennial census data  Year 2000 Summary File 3 (SF 3)  Long form, 1 in 6 households, random  Income, poverty  Educational attainment  Citizenship  Employment, workplace, disability  Transportation, travel time to work  Detailed housing attributes, housing value, residency five years previous  Languages spoken, ancestry  Tracts, block groups, NOT blocks 49 INF385T(28620) – Fall 2013 – Lecture 5

50. American Community Survey (ACS)  Replaces long-form questionnaire and SF3 data  Randomly selects about 3 million addresses each year to participate  Has rolling, 1-, 3-, and 5-year estimates and 90% confidence intervals  Add and subtract Margin of Error (MOE) to/from Estimate to get the confidence interval 50 INF385T(28620) – Fall 2013 – Lecture 5 50

51. ACS Data  Age  Sex  Race  Family and relationships  Income and benefits  Health insurance  Education  Veteran status  Disabilities  Where you work and how you get there  Where you live and how much you pay for certain essentials 51 INF385T(28620) – Fall 2013 – Lecture 5

52. ACS 1-year estimates  Most current  Data with populations 65,000+  Smallest sample size  Less reliable than 3–5 year  Best used when currency is more important than precision, or when analyzing large populations  Not available for tracts or block groups 52 INF385T(28620) – Fall 2013 – Lecture 5

53. ACS 3-year estimates  Data with populations 20,000+  Larger sample size than 1-year  More reliable than 1-year but less reliable than 5-year  Best used when analyzing smaller populations or geographies not available for 1-year estimates  Not available for tracts or block groups 53 INF385T(28620) – Fall 2013 – Lecture 5

54. ACS 5-year estimates  Data for all areas (tracts and block groups)  Largest sample size  Most reliable but least current  Best used when analyzing small populations, or when precision is more important than currency  2005–2009, 2006–2010, etc.  Note: 2006–2010 only available for county, city, town, place, American Indian Area, Alaska Native Area, Hawaiian Home Land, and tracts. Block group estimates are available only in the ACS Summary File. 54 INF385T(28620) – Fall 2013 – Lecture 5

55. Downloading block group data  http://www.census.gov/acs/www/data_documentation/summary_file/ http://www.census.gov/acs/www/data_documentation/summary_file/  Find the tables of interest and their sequence number in the "Sequenced Number and Table Number" spreadsheet (http://www2.census.gov/ acs2010_5yr/summaryfile/)http://www2.census.gov/ acs2010_5yr/summaryfile/  Download the sequences that contain those tables 55 INF385T(28620) – Fall 2013 – Lecture 5

56. Other census data  Economic census  Population estimates  Annual economic surveys  DataFerret  http://dataferrett.census.gov/ http://dataferrett.census.gov/ 56 INF385T(28620) – Fall 2013 – Lecture 5

57. GEOSPATIAL DATA SOURCES Lecture 5

58. Spatial data infrastructure  Federal Geographic Data Committee (FGDC)  This nationwide data publishing effort known as National Spatial Data Infrastructure (NSDI).  Established by presidential order  Responsible for standards, policies, web portals  FGDC activities are administered through the FGDC Secretariat, hosted by the US Geological Survey 58 INF385T(28620) – Fall 2013 – Lecture 5

59. Spatial data packaging  Metadata  Documentation enabling intelligent use and interpretation  Data contents  Provided by geographic area (political, statistical, tile) or seamlessly (with extraction by area)  Quality of geographic features  Vector maps are generalized for small-scale maps  Raster maps vary by pixel size (30m to a few inches) and color depth 8 bits to 24 bits per pixel  Coordinate system  File format  Download or web service 59 INF385T(28620) – Fall 2013 – Lecture 5

60. Classification of map layers  Earth as a system  Living things are on, under, or above the Earth’s surface  They depend on the Earth and its environment for life and well-being  They are organized in political, social, territorial, and other arrangements  Map layers  Physical features:  Earth’s surface and subsurface  Environmental features:  atmosphere, climate, and weather  Living thing populations:  people, animals, plants, and microbes  Organizational features:  political, legal, administrative, and ecosystem 60 INF385T(28620) – Fall 2013 – Lecture 5

61. National Map orthoimagery  http://nationalmap.gov/viewer.html http://nationalmap.gov/viewer.html  Replacing the digital orthophoto quadrangles  High-resolution, seamless images in UTM coordinates  Rectified to remove distortions  1m resolution with 0.5 m or 1 ft in urban areas, natural color 61 INF385T(28620) – Fall 2013 – Lecture 5

62.  http://ned.usgs.gov/ http://ned.usgs.gov/  Replaces the digital elevation model (DEM)  Seamless raster map with 30m resolution for nation and 10m or better in some areas Hillshade NED map for Rockville, MD 62 INF385T(28620) – Fall 2013 – Lecture 5 National Elevation Data (NED)

63.  http://nationalmap.gov/viewer.html/ http://nationalmap.gov/viewer.html/  Natural and man-made surface features  Collected from satellites in 1992, 2001, and 2006 63 INF385T(28620) – Fall 2013 – Lecture 5 Land cover

64.  http://nhd.usgs.gov/ http://nhd.usgs.gov/  Water bodies, lines, and points  Identifies segments (reaches) with network coding (flow and direction) 64 INF385T(28620) – Fall 2013 – Lecture 5 National Hydrography Dataset

65. USGS national water datasets  http://waterdata.usgs.gov/nwis/rt http://waterdata.usgs.gov/nwis/rt  Streamflow conditions  5,000 stream gages with telemetry transmits depth  Program estimates flow rate 65 INF385T(28620) – Fall 2013 – Lecture 5

66. Example geospatial sources  Government websites (examples)  http://data.gov/ http://data.gov/  http://www.geoplatform.gov/home/ http://www.geoplatform.gov/home/  http://nationalatlas.gov/ http://nationalatlas.gov/  http://nces.ed.gov/ccd/ - National Center for Education Statistics http://nces.ed.gov/ccd/  Universities  State clearinghouses  Local GIS departments  Libraries  For example, online business databases 66 INF385T(28620) – Fall 2013 – Lecture 5

67. Example geospatial sources  Commercial resources  (Esri, Google, engineering companies, etc.)  Historic GIS websites  http://www.nhgis.org/ http://www.nhgis.org/  http://www.aag.org/cs/projects_and_programs/hi storical_gis_clearinghouse http://www.aag.org/cs/projects_and_programs/hi storical_gis_clearinghouse  http://peoplemaps.esri.com/pittviewer/ http://peoplemaps.esri.com/pittviewer/ 67 INF385T(28620) – Fall 2013 – Lecture 5

68. Summary  Models of the Earth  Map coordinates  Map projections  US Census geographic files  US Census data files  Geospatial data sources 68 INF385T(28620) – Fall 2013 – Lecture 5