1. Review for Midterm Exam
GIS in Water Resources
Review for Midterm Exam

2. Data Models
A geographic data model is a structure for organizing geospatial data so that it can be easily stored and retrieved.
Geographic coordinates
Tabular attributes

3. Raster and Vector Data Vector Raster Point Line Polygon
Raster data are described by a cell grid, one value per cell
Vector
Raster
Point
Line
DRM
Zone of cells
Polygon

4. ArcGIS Geodatabase Workspace Geodatabase Feature Dataset Feature Class
Geometric
Network
Object Class
Relationship
Workspace

5. Geodatabase and Feature Dataset
A geodatabase is a relational database that stores geographic information.
A feature dataset is a collection of feature classes that share the same spatial reference frame.

6. Feature Class
A feature class is a collection of geographic objects in tabular format that have the same behavior and the same attributes.
Feature Class = Object class + spatial coordinates

7. Object Class
An object class is a collection of objects in tabular format that have the same behavior and the same attributes.
An object class is a table that has a unique identifier (ObjectID)
for each record

8. Relationship Relationship between spatial and non-spatial objects
Water quality data
(non-spatial)
Measurement station
(spatial)

9. National Hydro Data Programs
National Elevation Dataset
(NED)
National Hydrography Dataset
(NHD)
NED-Hydrology
Watershed Boundary Dataset

10. 1:250,000 Scale Soil Information

11. National Land Cover Dataset
Get the data:

12. National Water Information System
Web access to USGS water
resources data in real time

13. Arc Hydro Components Drainage System Hydro Network Time Series
GIS provides for synthesis of geospatial data with different formats
Drainage System
Hydro Network
Flow
Time
Time Series
Channel System
Hydrography

14. “Burning In” the Streams
Synthesis of Raster and Vector data
 Take a mapped stream network and a DEM
 Make a grid of the streams
 Raise the off-stream DEM cells by an arbitrary elevation
increment
 Produces "burned in" DEM streams = mapped streams + =

15. AGREE Elevation Grid Modification Methodology

16. Geodesy, Map Projections and Coordinate Systems
Geodesy - the shape of the earth and definition of earth datums
Map Projection - the transformation of a curved earth to a flat map
Coordinate systems - (x,y) coordinate systems for map data

17. Latitude and Longitude in North America
Austin:
(30°N, 98°W)
Logan:
(42°N, 112°W)
60 N
30 N
120 W
60 W
90 W
0 N

18. Length on Meridians and Parallels
(Lat, Long) = (f, l)
Length on a Meridian:
AB = Re Df
(same for all latitudes) R Dl
30 N R D C Re Df B
0 N Re
Length on a Parallel:
CD = R Dl = Re Dl Cos f
(varies with latitude) A

19. Example: What is the length of a 1º increment along
on a meridian and on a parallel at 30N, 90W?
Radius of the earth = 6370 km.
Solution:
A 1º angle has first to be converted to radians
p radians = 180 º, so 1º = p/180 = /180 = radians
For the meridian, DL = Re Df = 6370 * = 111 km
For the parallel, DL = Re Dl Cos f
= 6370 * * Cos 30
= 96.5 km
Parallels converge as poles are approached

20. Horizontal Earth Datums
An earth datum is defined by an ellipse and an axis of rotation
NAD27 (North American Datum of 1927) uses the Clarke (1866) ellipsoid on a non geocentric axis of rotation
NAD83 (NAD,1983) uses the GRS80 ellipsoid on a geocentric axis of rotation
WGS84 (World Geodetic System of 1984) uses GRS80, almost the same as NAD83

21. Vertical Earth Datums A vertical datum defines elevation, z
NGVD29 (National Geodetic Vertical Datum of 1929)
NAVD88 (North American Vertical Datum of 1988)
takes into account a map of gravity anomalies between the ellipsoid and the geoid

22. Coordinate System A planar coordinate system is defined by a pair
of orthogonal (x,y) axes drawn through an origin Y X
Origin
(xo,yo)
(fo,lo)

23. Universal Transverse Mercator
Uses the Transverse Mercator projection
Each zone has a Central Meridian (lo), zones are 6° wide, and go from pole to pole
60 zones cover the earth from East to West
Reference Latitude (fo), is the equator
(Xshift, Yshift) = (xo,yo) = (500000, 0) in the Northern Hemisphere, units are meters

24. UTM Zone 14
-99°
-102°
-96° 6°
Origin
Equator
-120°
-90 °
-60 °

25. ArcInfo 8 Reference Frames
Defined for a feature dataset in ArcCatalog
Coordinate System
Projected
Geographic
X/Y Domain
Z Domain
M Domain

26. X/Y Domain (Max X, Max Y) Long integer max value
of 231 = 2,147,483,645
(Min X, Min Y)
Maximum resolution of a point = Map Units / Precision
e.g. map units = meters, precision = 1000, then
maximum resolution = 1 meter/1000 = 1 mm on the ground

27. Four Points

28. One degree box and its four lines
Geographic Coordinates

29. One Degree Box in USGS Albers Projection

30. USGS Albers Projection

31. Area Calculation in USGS Albers
81.09 km km km
Area = km2
82.26 km
x = km2 2

32. North American Albers Projection

33. Area Calculation in North American Albers
76.64 km km km
Area = km2
77.89 km
X = 2
Take home message: Lengths of lines change but area is constant in Albers

34. Two fundamental ways of representing geography are discrete objects and fields.
The discrete object view represents the real world as objects with well defined boundaries in empty space.
(x1,y1)
Points
Lines
Polygons
The field view represents the real world as a finite number of variables, each one defined at each possible position.
DRM x y
f(x,y)
Continuous surface

35. Vector and Raster Representation of Spatial Fields

36. Numerical representation of a spatial surface (field)
Grid
TIN
Contour and flowline

37. Grid Datasets
Cellular-based data structure composed of square cells of equal size arranged in rows and columns.
The grid cell size and extent (number of rows and columns), as well as the value at each cell have to be stored as part of the grid definition.
Number of columns
Number of rows
Cell size

38. Raster Sampling
from Michael F. Goodchild. (1997) Rasters, NCGIA Core Curriculum in GIScience, posted October 23, 1997

39. The scale triplet Extent Spacing Support
From: Blöschl, G., (1996), Scale and Scaling in Hydrology, Habilitationsschrift, Weiner Mitteilungen Wasser Abwasser Gewasser, Wien, 346 p.

40. Raster Generalization
Largest share rule
Central point rule

41. Raster calculation – some subtleties
Resampling or interpolation (and reprojection) of inputs to target extent, cell size, and projection within region defined by analysis mask + =
Analysis mask
Analysis cell size
Analysis extent

42. Interpolation Apparent improvement in resolution may not be justified
Estimate values between known values.
A set of spatial analyst functions that predict values for a surface from a limited number of sample points creating a continuous raster.
Apparent improvement in resolution may not be justified

43. Topographic Slope Defined or represented by one of the following
Surface derivative z
Vector with x and y components
Vector with magnitude (slope) and direction (aspect)

44. - Direction of Steepest Descent
Hydrologic Slope
- Direction of Steepest Descent 30 30 67 56 49 52 48 37 58 55 22 67 56 49 52 48 37 58 55 22
Slope:

45. Eight Direction Pour Point Model32 16 8 64 4
128 1 2
Water flows in the direction of steepest descent

46. Filling in the Pits
DEM creation results in artificial pits in the landscape
A pit is a set of one or more cells which has no downstream cells around it
Unless these pits are filled they become sinks and isolate portions of the watershed
Pit filling is first thing done with a DEM

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

48. Cell to Cell Grid Network
Through the Landscape
Stream cell

49. Contributing Area Grid1 4 3 12 2 16 25 6 1 4 3 12 2 16 6 25
Drainage area threshold > 5 Cells

50. Delineation of Streams and Watersheds on a DEM

51. Watershed and Drainage Paths Delineated from 30m DEM
Automated method is more consistent than hand delineation

52. Stream Segments in a Cell Network1 3 2 4 5 6 5 5

53. Subwatersheds for Stream Segments
Same Cell Value

54. Vectorized Streams Linked Using Grid Code to Cell Equivalents

55. Delineated Catchments and Stream Networks
For every stream segment, there is a corresponding catchment
Catchments are a tessellation of the landscape through a set of physical rules

56. Raster Zones and Vector Polygons
One to one connection
DEM GridCode
Raster Zones 3 4 5
Catchment GridID
Vector Polygons

57. Area goes to Line Connectivity
For each catchment there is a unique drainage line
GridID is same on
both Catchment and
Drainage Line

58. Watershed
A watershed is the area draining to any point on the stream network
A new kind of connectivity: Area flows to a point on a line
Arc Hydro page 39 defines this concept

59. Connecting Drainage Areas to the Network
Area goes to
point on line

60. HydroID – a unique identifier of all Arc Hydro features
HydroIDs of Drainage Points
HydroIDs of Catchments

61. Area flows to point on line connectivity through GridID

62. Area flows to point on line connectivity through GridID

63. DrainageLine Feature Class Inter-connectivity using HydroID and NextDownID

64. Catchment Feature Class Inter-connectivity using HydroID and NextDownID

65. Hydrologic processes are different on hillslopes and in channels
Hydrologic processes are different on hillslopes and in channels. It is important to recognize this and account for this in models.
Drainage area can be concentrated or dispersed (specific catchment area) representing concentrated or dispersed flow.

66. Drainage Density Dd = L/A
EPA Reach Files
100 grid cell threshold
1000 grid cell threshold

67. Network Definition
A network is a set of edges and junctions that are topologically connected to each other.

68. Edges and Junctions Simple feature classes: points and lines
Network feature classes: junctions and edges
Edges can be
Simple: one attribute record for a single edge
Complex: one attribute record for several edges in a linear sequence
A single edge cannot be branched
No!!

69. Polylines and Edges

70. Junctions Junctions exist at all points where edges join
If necessary they are added during network building (generic junctions)
Junctions can be placed on the interior of an edge e.g. stream gage
Any number of point feature classes can be built into junctions on a single network

71. Connectivity Table p. 132 of Modeling our World J125 Junction
Adjacent Junction and Edge
J123
J124, E1
J124
J123, E1
J125, E2
J126, E3
J125
J124, E2
J126
J124, E3 E2
J124 E3 E1
J123
J126
This is the “Logical Network”

72. Flow to a sink

73. Network Tracing on the Guadalupe Basin

74. Linear Referencing
Where are we on a line?

75. Addressing