Introduction to GIS

1. Introduction to GIS David R. Maidment Center for Research in Water Resources University of Texas at Austin http://www.ce.utexas.edu/prof/maidment

2. Presentation Outline • Using GIS to connect hydrology and meteorology • Representation of spatial objects in GIS • Terrain analysis using Digital Elevation Models • Geodesy and map projections

3. Hydrologic Cycle: Connecting the Land Surface with the Atmosphere

4. Connecting Hydrology and Meteorology • Two Spatial Scales • Drainage basin scale for consideration of severe storms and flood (Nexrad radar precipation as input, flood runoff as output) • Regional or global scale for consideration of climate change (Global climate models as input, time series of river flows as output)

5. Regional flood analysis in Houston Study region

6. Nexrad Rainfall for Storm of Oct 1994

7. Discharge in Buffalo Bayou at KatyOctober, 1994 storm

8. Calibrated Flow with HEC-HMS

9. Global Runoff (mm/yr) According to NCAR’s CCM3.2 Global Climate Model (GCM)

10. GTOPO30 - 30” Digital Elevation Model of the Earth Source: http://edcwww.cr.usgs.gov/landdaac/gtopo30/gtopo30.html

11. Drainage in North America Source: http://edcwww.cr.usgs.gov/landdaac/gtopo30/hydro/namerica.html

12. Drainage Basins of North America Source: http://edcwww.cr.usgs.gov/landdaac/gtopo30/hydro/na_basins.html

13. Amazon River MacKenzie River Congo River Yangtze River Streamflow Hydrographs for Large Basins Runoff Input from Climate Model Streamflow Output at River Mouth

14. A Fundamental Dilemma • Land Surface Hydrology has: • drainage patterns organized by rivers and watersheds which are spatially discrete • analysis in Cartesian coordinates (x,y,z) • Atmospheric Science has: • circulation patterns which are spatially continuous over the earth • analysis in Geographic coordinates (f, l, z) GIS can be used to connect these two spatial frameworks

15. Presentation Outline • Using GIS to connect hydrology and meteorology • Representation of spatial objects in GIS • Terrain analysis using Digital Elevation Models • Geodesy and map projections

16. Discrete and Continuous Space Discrete Space: Vector GIS Continuous Space: Raster GIS

17. Geospatial Database: a set of compatible data layers or themes

18. Spatial Data: Vectorformat Vector data are defined spatially: (x1,y1) Point - a pair of x and y coordinates vertex Line - a sequence of points Node Polygon - a closed set of lines

19. Feature Attribute Table Fields Records

20. Relational Linkages Spatial Attributes Water Right Locations Descriptive Attributes

21. Locations on the Stream Network Digital Stream Network Connects Control Point Locations

22. Watersheds defined using a Digital Elevation Model

23. Spatial Data: Rasterformat Cell size Number of rows NODATA cell (X,Y) Number of Columns Definition of a Grid in GIS

24. Points as Cells

25. Line as a Sequence of Cells

26. Polygon as a Zone of Cells

27. Raster Vector Real World Raster-Vector Data Model

28. Presentation Outline • Using GIS to connect hydrology and meteorology • Representation of spatial objects in GIS • Terrain analysis using Digital Elevation Models • Geodesy and map projections

29. Study Region in West Austin Hog Pen Ck 4 km 4 km

30. Watershed Delineation by Hand Digitizing Watershed divide Outlet Drainage direction

31. 30 Meter MeshStandard for 1:24,000 Scale Maps

32. DEM Elevations 720 720 Contours 740 720 700 680 740 720 700 680

33. DEM Elevations Contours 700 680

34. 32 64 128 16 1 8 4 2 Eight Direction Pour Point Model

35. 67 56 49 53 44 37 58 55 22 Direction of Steepest Descent 1 1 67 56 49 53 44 37 58 55 22 Slope:

36. 2 2 4 4 8 1 2 4 8 4 128 1 2 4 8 2 1 4 4 4 1 1 1 2 16 Flow Direction Grid

37. Austin West 30 Meter DEMElevations in meters ftp://ftp.tnris.state.tx.us/tnris/demA.html

38. 32 64 128 16 1 8 4 2 Flow Direction Grid

39. Grid Network

40. Flow Accumulation Grid 0 0 0 0 0 0 0 0 0 0 0 3 2 2 0 3 2 0 0 2 0 0 1 0 0 11 0 1 0 11 0 0 0 1 15 0 0 1 0 15 1 0 2 5 24 2 5 0 1 24 Link to Grid calculator

41. 0 0 0 0 0 0 3 2 2 0 0 1 0 0 11 0 0 0 1 15 1 0 2 5 24 Flow Accumulation > 5 Cell Threshold

42. Stream Network for 5 cell Threshold Drainage Area 0 0 0 0 0 3 2 0 0 2 0 0 1 0 11 0 0 1 0 15 2 5 0 1 24

43. Streams with 200 cell Threshold(>18 hectares or 13.5 acres drainage area)

44. Watershed Outlet

45. Watershed Draining to This Outlet

46. Watershed andDrainage PathsDelineated from 30m DEM Automated method is more consistent than hand delineation

47. DEM Data Sources • 30m DEMs from 1:24,000 scale maps (urban watersheds) • 3" (100m) DEMs from 1:250,000 scale maps (rural watersheds) • 15" (500m) DEM for the US resampled from 3” DEM (large drainage basins) • 30" (1km) DEM of the earth (GTOPO30)

48. Presentation Outline • Using GIS to connect hydrology and meteorology • Representation of spatial objects in GIS • Terrain analysis using Digital Elevation Models • Geodesy and map projections

49. Shape of the Earth It is actually a spheroid, slightly larger in radius at the equator than at the poles We think of the earth as a sphere

50. Geographic Coordinates (f, l, z) • Latitude (f) and Longitude (l) defined using an ellipsoid, an ellipse rotated about an axis • Elevation (z) defined using geoid, a surface of constant gravitational potential • Earth datums define standard values of the ellipsoid and geoid