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

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

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

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

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.

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

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

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

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

1:250,000 Scale Soil Information http://www.ftw.nrcs.usda.gov/stat_data.html

National Land Cover Dataset http://landcover.usgs.gov/nationallandcover.html Get the data: http://seamless.usgs.gov/

National Water Information System Web access to USGS water resources data in real time http://waterdata.usgs.gov/usa/nwis/

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

“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 + =

AGREE Elevation Grid Modification Methodology

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

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

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

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 = 3.1416/180 = 0.0175 radians For the meridian, DL = Re Df = 6370 * 0.0175 = 111 km For the parallel, DL = Re Dl Cos f = 6370 * 0.0175 * Cos 30 = 96.5 km Parallels converge as poles are approached

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

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

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)

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

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

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

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

Four Points

One degree box and its four lines Geographic Coordinates

One Degree Box in USGS Albers Projection

USGS Albers Projection

Area Calculation in USGS Albers 81.09 km 111.79 km 111.79 km Area = 9130.6 km2 82.26 km 82.26 + 81.09 x 111.79 = 9130.5 km2 2

North American Albers Projection

Area Calculation in North American Albers 76.64 km 118.17 km 118.17 km Area = 9130.6 km2 77.89 km 77.89 + 76.64 X 118.17 = 9130.4 2 Take home message: Lengths of lines change but area is constant in Albers

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

Vector and Raster Representation of Spatial Fields

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

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

Raster Sampling from Michael F. Goodchild. (1997) Rasters, NCGIA Core Curriculum in GIScience, http://www.ncgia.ucsb.edu/giscc/units/u055/u055.html, posted October 23, 1997

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

Raster Generalization Largest share rule Central point rule

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

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

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)

- 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:

Eight Direction Pour Point Model 32 16 8 64 4 128 1 2 Water flows in the direction of steepest descent

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

Flow Direction Grid 32 16 8 64 4 128 1 2

Cell to Cell Grid Network Through the Landscape Stream cell

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

Delineation of Streams and Watersheds on a DEM

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

Stream Segments in a Cell Network 1 3 2 4 5 6 5 5

Subwatersheds for Stream Segments Same Cell Value

Vectorized Streams Linked Using Grid Code to Cell Equivalents

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

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

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

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

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

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

Area flows to point on line connectivity through GridID

Area flows to point on line connectivity through GridID

DrainageLine Feature Class Inter-connectivity using HydroID and NextDownID

Catchment Feature Class Inter-connectivity using HydroID and NextDownID

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.

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

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

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!!

Polylines and Edges

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

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”

Flow to a sink

Network Tracing on the Guadalupe Basin

Linear Referencing Where are we on a line?

Addressing