1. Lecture 4 Understanding Coordinate Systems

2. Geographic Coordinate systems GCS Spherical Ellipsoidal Curved

3. Projected coordinate systems GCS PCS (PCS) 2D Flat Planar Cartesian

4. GCS has angular units of measure Degrees  360 per circle  Decimal degrees  Degree, minute, second Radians  2 pi per circle  ~6.3 per circle (~57 degrees each) Gradian  400 per circle Gon  Same as gradians  To some grad = degree

5. X - Y + X + Y + X - Y - X + Y - X Data usually here Y PCS has linear units of measure Linear units  Meters  Feet X and Y coordinates Length, angles, and areas are constant

6. Map projection Math to transform GCS

7. Map projection Plate Carrée projection Math to transform GCS to PCS Flattening the earth – round to flat Distortions make geographers SADD  Shape, Area, Distance, and Direction

8. PCS properties example Name – NAD 1983 UTM Zone 11N GCS – NAD 1983 Map Projection – Mercator Projection parameters  Central meridian, latitude of origin, scale factor, false easting Linear unit of measure (i.e., meters)

9. Geographic coordinate systems Mathematical model of a planetary body - spheroid Parameters describe the spheroid shape  Smooth, without imperfections GCS for earth, planets, and more EarthMarsIO

10. GCS properties Spheroid  Major and minor axis  Units (lat/long, radians, grads)

11. GCS properties Spheroid  Major and minor axis  Units (lat/long, radians, grads) Datum  Spheroid’s position in relation to actual earth  Local datum: spheroid touches edge of earth, good fit there Great fit here Bad fit here Local datum

12. GCS properties Spheroid  Major and minor axis  Units (lat/long, radians, grads) Datum  Spheroid’s position in relation to actual earth  Local datum: spheroid touches edge of earth, good fit there  Earth-centered: spheroid and earth center match Great fit here Bad fit here Local datum All around best fit for the entire planet Earth-centered datum

13. GCS properties example Name  European Datum 1950 Datum  European Datum 1950  Spheroid International 1924 Prime Meridian  Greenwich Angular unit of measure  Degrees

14. GCS with a local datum Spheroid

15. GCS with a local datum Datum  Spheroid’s position in relation to actual earth

16. GCS with a local datum Datum  Spheroid’s position in relation to actual earth

17. GCS with a local datum Datum  Spheroid’s position in relation to actual earth

18. GCS with a local datum Datum  Spheroid’s position in relation to actual earth

19. GCS with a local datum Datum  Spheroid’s position in relation to actual earth

20. GCS with a local datum Datum  Spheroid’s position in relation to actual earth  Local datum: spheroid touches edge of earth, good fit there  Bad fit on the other side

21. GCS with an Earth Centered datum Spheroid

22. GCS with an Earth Centered datum Datum  Spheroid’s center matched to earth center

23. GCS with an Earth Centered datum Datum  Spheroid’s center matched to earth center

24. GCS with an Earth Centered datum Datum  Spheroid’s center matched to earth center

25. GCS with an Earth Centered datum Datum  Spheroid’s center matched to earth center

26. GCS with an Earth Centered datum Datum  Spheroid’s center matched to earth center

27. GCS with an Earth Centered datum Datum  Spheroid’s center matched to earth center  Best fit all around the earth

28. As measurement gets better, new GCS are defined  NAD27 – parameters defined in 1866 (log tables)  NAD83 – parameters defined in 1979 (pre-GPS)  WGS84 – parameters defined in 1984 (GPS) Common GCS parameters in use today (US) North American Datum 1927 North American Datum 1983 World Geodetic Survey 1984

29. Warning: different geographic coordinate system…

30. Geographic transformation Math to transform from one GCS to another NAD 27 34 Degrees 3 Minutes 23.1 Seconds North ESRI-Redlands 117 Degrees 11 Minutes 39.2 Seconds West

31. Geographic transformation Math to transform from one GCS to another Changing GCS changes the lat/long for same point The same spot on earth has differing coordinates NAD 27NAD 83 34 Degrees 3 Minutes 23.14 Seconds North ESRI-Redlands 117 Degrees 11 Minutes 42.36 Seconds West 34 Degrees 3 Minutes 23.1 Seconds North ESRI-Redlands 117 Degrees 11 Minutes 39.2 Seconds West

32. ArcMap’s GCS and PCS behavior Data frame - has both Spatial data - has GCS, may have PCS Metadata - prj, XML, mdb, or none Tools that help

33. On-the-fly projection ArcMap data frames have a GCS and a PCS  You should set them  If not set, data frames take first layer’s GCS/PCS Data frame: Bonne PCS

34. On-the-fly projection ArcMap data frames have a GCS and a PCS  You should set them  If not set, data frames take first layer’s GCS/PCS If needed, new layers are projected on-the-fly (to match)  If no CS metadata, new layer cannot be projected on- the-fly Input layer: Robinson PCSData frame: Bonne PCS ArcMap projects data on-the-fly into a data frame

35. GCS and PCS metadata for spatial data Stored in internal geodatabase tables Stored in projection files  Shapefiles can have a.prj text file (e.g., streets.prj)  Coverages can have a prj.adf text file (e.g., /rivers/prj.adf) Stored optionally in XML files created by ArcCatalog Non-native ESRI datasets use various other formats

36. Warning! GCS and PCS metadata is NOT required You might get data that is missing its coordinate system metadata If researched and discovered, you can add it If not, use Spatial Adjustment to move the data into place

37. Spatial reference problems and solutions ProblemSolution  You know the coordinate system information, but it is missing  Define Projection tool  The PCS is defined correctly, but is not the one you need  Project tool or data frame project on-the-fly  The GCS is defined, but it is not NAD27 or NAD83  Project tool or set a geographic transformation in the data frame properties