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					   Introduction to GIS
      David R. Maidment
Center for Research in Water Resources
     University of Texas at Austin
http://www.ce.utexas.edu/prof/maidment
                      FOR RES E
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         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
Hydrologic Cycle: Connecting the
Land Surface with the Atmosphere
    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)
Regional flood analysis in Houston


Study region
Nexrad Rainfall for Storm of Oct 1994
Discharge in Buffalo Bayou at Katy
       October, 1994 storm
Calibrated Flow with HEC-HMS
     Global Runoff (mm/yr)




According to NCAR’s CCM3.2 Global Climate Model (GCM)
    GTOPO30 - 30” Digital
  Elevation Model of the Earth




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




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




Source: http://edcwww.cr.usgs.gov/landdaac/gtopo30/hydro/na_basins.html
Streamflow Hydrographs for Large Basins
 Runoff Input from Climate Model   Streamflow Output at River Mouth




                                              MacKenzie River
                                         Yangtze River
      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
         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
Discrete and Continuous Space

         Discrete Space: Vector GIS




         Continuous Space: Raster GIS
  Geospatial Database: a set of
compatible data layers or themes
    Spatial Data: Vector format
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
          Feature Attribute Table
          Fields

Records
  Relational Linkages

                 Spatial Attributes




Water Right
 Locations
              Descriptive Attributes
Locations on the Stream Network
        Digital Stream Network
     Connects Control Point Locations
Watersheds defined using a
 Digital Elevation Model
Spatial Data: Raster format
                                  Cell size

Number
  of
 rows
                                NODATA cell
    (X,Y)
            Number of Columns

  Definition of a Grid in GIS
Points as Cells
Line as a Sequence of Cells
Polygon as a Zone of Cells
Raster-Vector Data Model

              Raster



              Vector




              Real World
         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
Study Region in West Austin

                           Hog Pen Ck

                    4 km




          4 km
   Watershed Delineation by Hand Digitizing



Watershed divide




         Drainage direction          Outlet
      30 Meter Mesh
Standard for 1:24,000 Scale Maps
DEM Elevations
      720     720
                      Contours
                      740

                      720

                      700

                      680

740 720 700     680
DEM Elevations   Contours

                   700




                   680
Eight Direction Pour Point Model

        32    64   128


        16          1


         8    4     2
   Direction of Steepest Descent
         1               1

         67   56   49    67   56   49

         53   44   37    53   44   37

         58   55   22    58   55   22

       67  44
                16.26
                         67  53
Slope:                            14
           2                1
Flow Direction Grid

            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
Austin West 30 Meter DEM
             Elevations in meters
 ftp://ftp.tnris.state.tx.us/tnris/demA.html
             Flow Direction Grid



32 64 128

16       1

8    4   2
Grid Network
             Flow Accumulation Grid

0    0       0             0   0   0   0   0    0    0

0        3        2        2   0   0   3   2    2    0
                           0       0   0   11   0    1
0    0       11                1
0                 1            0   0   0   1    15   0
     0                 15
0        2        5                0   2   5    24   1
                               1
                      24

Link to Grid calculator
Flow Accumulation > 5 Cell Threshold

          0   0   0    0    0

          0   3   2    2    0

          0   0   11   0    1

          0   0   1    15   0

          0   2   5    24   1
Stream Network for 5 cell
Threshold Drainage Area
   0   0       0            0    0

   0       3       2        2    0

                            0
   0   0                         1
               11
   0             1               0
       0
                            15
   0       2       5
                                 1
                       24
Streams with 200 cell Threshold
  (>18 hectares or 13.5 acres drainage area)
Watershed Outlet
Watershed Draining to This Outlet
      Watershed and Drainage Paths
       Delineated from 30m DEM




Automated method is more consistent than hand delineation
        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)
         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
       Shape of the Earth

We think of the       It is actually a spheroid,
earth as a sphere    slightly larger in radius at
                    the equator than at the poles
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
                           Ellipse
An ellipse is defined by:
                                           Z
Focal length = 
Distance (F1, P, F2) is
constant for all points
on ellipse                                 b
When  = 0, ellipse = circle           O           a        X
                                F1                   F2
For the earth:
Major axis, a = 6378 km
Minor axis, b = 6357 km
Flattening ratio, f = (a-b)/a    P
                    ~ 1/300
 Ellipsoid or Spheroid
Rotate an ellipse around an axis
                Z


             b
           a O a            Y

   X


          Rotational axis
Representations of the Earth
     Mean Sea Level is a surface of constant
     gravitational potential called the Geoid
Sea surface                         Ellipsoid




                                         Earth surface



 Geoid
Definition of Elevation
               Elevation Z
          P
                 z = zp
           •              Land Surface
                z=0

Mean Sea level = Geoid

Elevation is measured from the Geoid
          Coordinate System
     A planar coordinate system is defined by a pair
     of orthogonal (x,y) axes drawn through an origin

                                      Y




                     Origin                             X

                                       (xo,yo)
(fo,lo)
 Earth to Globe to Map




     Map Scale:           Map Projection:
Representative Fraction       Scale Factor

  = Globe distance            Map distance
                          =
    Earth distance            Globe distance
    (e.g. 1:24,000)            (e.g. 0.9996)
         Conic Projections
(Albers Equal Area, Lambert Conformal Conic)
      Cylindrical Projections
        (Universal Transverse Mercator)




Transverse



                             Oblique
       Azimuthal
(Lambert Azimuthal Equal Area)
       Presentation Summary
• Using GIS to connect hydrology and
  meteorology
• Representation of spatial objects in GIS
• Terrain analysis using Digital Elevation
  Models
• Geodesy and map projections

				
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