SOC 4650 & SOC 5650 - Lecture 10

Slides for Lecture 10 of the Saint Louis University Course Introduction to GIS. These slides introduce concepts related to projecting spatial data, including projected coordinate systems and techniques for projecting tabular data that includes x,y coordinates.

Transcript

1. PROJECTIONS INTRO TO GISC CHRISTOPHER PRENER, PH.D. SPRING 2019 WEEK 10 LECTURE 10
2. AGENDA 1. Front Matter 2. Projections Overview 3. Working with Projections in R 4. Working with Projections in ArcMap 5. Back Matter INTRO TO GISC / WEEK 10 / LECTURE 10
3. 1 FRONT 
 MATTER
4. April gets very busy for this class - please plan your time mindfully! Final project instructions now posted! Lab-08 is due this Wednesday! 1. FRONT MATTER ANNOUNCEMENTS Lab-09 and a check-in for the final project are due next Monday!
5. PROJECTIONS OVERVIEW 2
6. ▸ We are used to thinking about earth as a sphere… ▸ …but it is not actually a perfect sphere. ▸ We therefore use models of earth’s shape for mapping and navigation. 2. PROJECTIONS OVERVIEW CONCEPTUALIZING EARTH
7. KEY TERM An ellipsoid (or 
 spheroid) is a mathematical
 model depicting the earth
 in a three-dimensional space. GRS 1980 and WGS 1984 are most common. Source: Maher 2010, p. 170
8. KEY TERM A datum is a collection
 of known locations used
 to locate data on an ellipsoid. 
 NAD 1983 and WGS 1984 are two common datums. Source: Maher 2010, p. 171
9. KEY TERM A geographic coordinate
 system is combination of
 an ellipsoid, a datum, a prime meridian, and a specified unit of measure. NAD 1983 and WGS 1984 are two systems. Source: Maher 2010, p. 171
10. 2. PROJECTIONS OVERVIEW WHY MULTIPLE SYSTEMS? ▸ In attempting to be useful everywhere, the WGS 1984 system is not a perfect fit for many places on earth. ▸ Local models are therefore preferable for continental or regional mapping. ▸ The NAD 1983 system is meant to better fit the specific shape of earth in North America
11. 2. PROJECTIONS OVERVIEW BUT MAPS ARE NOT 3D This presents a challenge for print and computer mapping, where our surfaces are only capable of conveying two dimensional space.
12. 2. PROJECTIONS OVERVIEW BUT MAPS ARE NOT 3D However, when we transform three dimensional data into two dimensional space, we will inevitably distort them.
13. ▸ Carl Fredrich Gauss • Born 1777, died 1855 • Mathematician from what is now Germany who made significant contributions to many fields within mathematics ▸ His “remarkable theorem” holds that spheres and planes are not isometric - we cannot flatten a sphere while preserving distance, shape, and area. 2. PROJECTIONS OVERVIEW THEOREMA EGREGIUM
14. KEY TERM A projected coordinate
 system transforms data so
 that they can be mapped in
 two-dimensional space. Source: Maher 2010, p. 174
15. 2. PROJECTIONS OVERVIEW PROJECTIONS & CARTOGRAPHY
16. 2. PROJECTIONS OVERVIEW PROJECTIONS & CARTOGRAPHY
17. PROJECTED COORDINATE SYSTEMS ▸ Projections have properties that they prioritize: • Conformal projections preserve shape • Equal area projections preserve area • Equidistant projections preserve distance • True direction projections preserve direction
 ▸ Some “compromise projections” attempt to strike a balance between properties, but many prioritize one at the expense of the others. 2. PROJECTIONS OVERVIEW
18. MERCATOR PROJECTION
19. MERCATOR DISTORTIONS 2. PROJECTIONS OVERVIEW
20. MERCATOR DISTORTIONS 2. PROJECTIONS OVERVIEW
21. MERCATOR DISTORTIONS 2. PROJECTIONS OVERVIEW https://thetruesize.com
22. 2. PROJECTIONS OVERVIEW CYLINDRICAL EQUAL AREA PROJECTION
23. AZIMUTHAL EQUIDISTANT PROJECTION
24. GALL STENOGRAPHIC PROJECTION
25. PROJECTIONS COMPARED NAD 1983 NAD 1983 / UTM 15N NAD 1983 / MO State Plan East
26. “LEVELS” OF PROJECTION ▸ Macro - Continental or worldwide extents ▸ Meso - State or Several State extents ▸ Regional - Counties or City extent ▸ Micro - City or Neighborhood extent 2. PROJECTIONS OVERVIEW
27. MACRO-LEVEL PROJECTIONS (CONTINENT) Geographic Coordinate System - NAD 1983
28. MACRO-LEVEL PROJECTIONS (CONTINENT) Projected Coordinate System - Albers Conical Equal Area
29. MACRO-LEVEL PROJECTIONS (CONTINENT) Projected Coordinate System - Lambert Conformal Conic Projection
30. MACRO-LEVEL PROJECTIONS (CONTINENT) Albers Lambert NAD 1983
31. MESO-LEVEL PROJECTIONS (STATE) Geographic Coordinate System - NAD 1983 Centered on -97.4472,38.3675
32. MESO-LEVEL PROJECTIONS (STATE) Projected Coordinate System - Albers Conical Equal Area, Contiguous USA Centered on -97.4472,38.3675
33. MESO-LEVEL PROJECTIONS (STATE) Projected Coordinate System - UTM 15N Centered on -97.4472,38.3675
34. MESO-LEVEL PROJECTIONS (STATE) Projected Coordinate System - UTM 16N Centered on -97.4472,38.3675
35. MESO-LEVEL PROJECTIONS (STATE) Albers NAD 1983 UTM 15N UTM 16N
36. MESO-LEVEL PROJECTIONS (STATE) Albers NAD 1983 UTM 15N UTM 16N
37. REGIONAL PROJECTIONS Geographic Coordinate System - NAD 1983 St. Louis Metropolitan Area Centered on -90.4462,38.6373
38. REGIONAL PROJECTIONS Projected Coordinate System - Albers Conical Equal Area Centered on -90.4462,38.6373 St. Louis Metropolitan Area
39. REGIONAL PROJECTIONS Projected Coordinate System - UTM 15N Centered on -90.4462,38.6373 St. Louis Metropolitan Area
40. REGIONAL PROJECTIONS Projected Coordinate System - State Plane (Missouri East) Centered on -90.4462,38.6373 St. Louis Metropolitan Area
41. REGIONAL PROJECTIONS Albers NAD 1983 UTM 15N State 
 Plane St. Louis Metropolitan Area
42. REGIONAL PROJECTIONS Albers NAD 1983 UTM 15N State 
 Plane St. Louis Metropolitan Area
43. MICRO-LEVEL PROJECTIONS (NEIGHBORHOOD) Centered on -90.2288,38.6313 Geographic Coordinate System - NAD 1983 Midtown Neighborhood in St. Louis
44. MICRO-LEVEL PROJECTIONS (NEIGHBORHOOD) Projected Coordinate System - Albers Conical Equal Area Midtown Neighborhood in St. Louis Centered on -90.2288,38.6313
45. MICRO-LEVEL PROJECTIONS (NEIGHBORHOOD) Centered on -90.2288,38.6313 Projected Coordinate System - UTM 15N Midtown Neighborhood in St. Louis
46. MICRO-LEVEL PROJECTIONS (NEIGHBORHOOD) Centered on -90.2288,38.6313 Projected Coordinate System - State Plane (Missouri East) Midtown Neighborhood in St. Louis
47. MICRO-LEVEL PROJECTIONS (NEIGHBORHOOD) Albers NAD 1983 UTM 15N State Plane Midtown Neighborhood in St. Louis
48. MICRO-LEVEL PROJECTIONS (NEIGHBORHOOD) Albers NAD 1983 UTM 15N State Plane Midtown Neighborhood in St. Louis
49. “LEVELS” OF PROJECTION ▸ Macro - Continental or worldwide extents - Geographic Coordinates or Albers/Lambert Projections ▸ Meso - State or Several State extents - Albers/Lambert or UTM ▸ Regional - Counties or City extent - UTM or State Plane ▸ Micro - City or Neighborhood extent - State Plane 2. PROJECTIONS OVERVIEW
50. 11 11 17 17 12 12 16 16 14 14 13 13 15 15 18 18 11 11 12 12 16 16 13 13 18 18 15 15 17 17 14 14 11 11 15 15 14 14 12 12 16 16 18 18 13 13 17 17 10 10 19 19 10 10 14 14 15 15 13 13 16 16 12 12 17 17 19 19 11 11 18 18 9 9 9 9 10 10 19 19 10 10 20 20 19 19 20 20 10 10 IDENTIFYING UTM ZONES
51. IDENTIFYING STATE PLANE REGIONS
52. IDENTIFYING STATE PLANE REGIONS Missouri 
 West Missouri 
 Central Missouri 
 East
53. IDENTIFYING STATE PLANE REGIONS FIPS 2403 FIPS 2402 FIPS 2401
54. WORKING WITH PROJECTIONS IN R 3
55. ▸ René Descartes • Born 1596, died 1650 • French mathematician and philosopher whose scientific work was done in the Netherlands ▸ Pioneered technique for locating points and shapes relative to axes using ordered pairs (like an x and a y coordinate) 3. WORKING WITH PROJECTIONS IN R CARTESIAN COORDINATES
56. KEY TERM Projecting data is the
 process of taking tabular
 data containing x and y 
 coordinates and covering it to geometric data so that it may be mapped.
57. 3. WORKING WITH PROJECTIONS IN R CONCEPTUALIZING PROJECTING id a x y 1 2 3 4 5
58. 3. WORKING WITH PROJECTIONS IN R CONCEPTUALIZING PROJECTING id a x y 1 2 3 4 5 id a geometry 1 2 3 4 5 ➜
59. 3. WORKING WITH PROJECTIONS IN R CONCEPTUALIZING PROJECTING Use to map point data stored in a
 tabular file format (e.g. a csv file) ➜ 1 2 5 3 4 id a geometry 1 2 3 4 5
60. CHECK GEOMETRY COLUMN
61. CHECK GEOMETRY COLUMN
62. 3. WORKING WITH PROJECTIONS IN R CHECK GEOMETRY COLUMN
63. ? 3. WORKING WITH PROJECTIONS IN R PROJECTIONS IN R ▸ If you’re using leaflet, make sure your data are in WGS 1984 (EPSG code 4326) ▸ Make sure you transform all layers into same coordinate system. ▸ It can be hard to guess what projected coordinate system x and y columns were created in. ▸ Writing coordinate systems can be tricky - verify that ArcGIS Pro reads shapefiles’ coordinate systems correctly! What are some challenges with projections in R?
64. ? 3. WORKING WITH PROJECTIONS IN R PROJECTIONS IN R ▸ If you’re using leaflet, make sure your data are in WGS 1984 (EPSG code 4326) ▸ Make sure you transform all layers into same coordinate system. ▸ It can be hard to guess what projected coordinate system x and y columns were created in. ▸ Writing coordinate systems can be tricky - verify that ArcGIS Pro reads shapefiles’ coordinate systems correctly! ▸ Longitude is your x value, and latitude is your y value What are some challenges with projections in R?
65. WORKING WITH PROJECTIONS IN ARCMAP 4
66. 5 BACK 
 MATTER
67. AGENDA REVIEW 2. Projections Overview 3. Working with Projections in R 4. Working with Projections in ArcMap 5. BACK MATTER
68. REMINDERS 5. BACK MATTER Lab-08 is due this Wednesday! Lab-09 and a check-in for the final project are due next Monday!