Introduction to Geographic Information Systems and Sample Applications

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Introduction to Geographic Information
Systemsand Sample Applications
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Overview

• Role of a GIS
• Parts of a GIS
• Spatial Data
• Relational Databases
• Geodesy and Map Projections
• ArcView and Sample Applications
• Scale and Resolution

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What is GIS????

• Standard definition
• An organized collection of computer hardware,
  software, geographic data, and personnel designed
  to efficiently capture, store, update,
  manipulate, analyze, and display all forms of
  geographically referenced information.
• Sound efficient??????

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GIS Simplified

• A computer-based tool for mapping and analyzing
  things.

• Geospatial Database a set of compatible data
  layers or themes

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The Role of GIS

• The advanced modeling programs and technologies
  used in water resources studies are increasingly
  GIS-based.
• Examples include
• Floodplain Assessments
• Land Use Planning
• Demographic and Economic Data
• Hydrologic and Water Quality Data Display
• Rainfall Analysis with NEXRAD Radar

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Digital Hydrologic / Hydraulic Processing
HEC-RAS Water surface profiles
HEC-HMS Flood discharge
HEC-GeoHMS
HEC-GeoRAS
ArcView Digital Elevation Model
ArcView Flood plain maps
Digital Map Database
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Parts of a GIS

• A GIS should be able to

• Take in spatial data - both maps and attributes
• Establish logical linkages between the data
  elements
• Put data into a storage system in which the data,
  and the places on the map that the data
  represents, are directly linked
• Perform analysis
• Produce and display information

• Take in spatial data - both maps and attributes
• Establish logical linkages between the data
  elements
• Put data into a storage system in which the data,
  and the places on the map that the data
  represents, are directly linked
• Perform analysis
• Produce and display information

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Spatial Data

• Spatial data is what goes into a GIS
• Maps are one of the most common forms of spatial
  data
• Features represented by areas
• Alphanumeric data to describe areas
• Descriptive data is known as attributes

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Attributes

• GIS stores more than just maps
• Relationship between map features and attributes
  within a GIS
• Dynamic interactive maps

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Data Entry and Storage

• Store data in a logical way
• Maps and data are stored in digital form
• Digital layers with attributes attached
• Layers are stored together in a relational
  database using a database management system
  (DBMS).

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Database Management System

• Inside the DBMS, spatial data is stored as
  digital layers with their associated attributes

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Analysis

• Why should spatial data be stored in a GIS?
• Want to use the power of the computer to ask
  questions of the spatial data
• Analyze data and produce new information
• Convey technical data non-technically

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Discrete and Continuous Space
Discrete Space Vector GIS Lumped models
Continuous Space Raster GIS, Tin Distributed
models
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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
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River Reaches
Flow along lines through the landscape
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River Basins
Hydrologic features containing several different
types of flow processes
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Spatial Data Grid (Raster) format
Raster data are described by a cell grid, one
value per cell
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NEXRAD Rainfall Intensity Image October 18, 1994
_at_ 300 AM (CST)
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NEXRAD Rainfall Intensity Image October 18, 1994
_at_ 400 AM (CST)
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Raster and Vector Data
Vector
Raster
Point
Line
Zone of cells
Polygon
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Points as Cells
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Line as a Sequence of Cells
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Polygon as a Zone of Cells
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Vector Data

• Uses positions to represent real world entities
• Points, lines, polygons

Reservoir and Highway
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Raster Data

• Samples attributes at fixed intervals
• List of numbers, one number per cell

Reservoir and Highway
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Hydrologic Cycle
Atmospheric water
Surface water
Subsurface water
Connecting processes in the hydrologic cycle
involves linking spatial features of various kinds
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Concept Summary

• A region can be considered spatially discrete or
  spatially continuous
• Discrete space is represented by features (vector
  data) and continuous space by elements or
  cells(raster data)
• Atmospheric water, surface water and subsurface
  water have a variety of continuous and discrete
  space representations with different boundaries

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Levels of Analysis Relational Database
Relational Linkages
Spatial Attributes
Water Right Locations
Descriptive Attributes
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Feature Attribute Table
Fields
Records
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Value Attribute Table
Attributes of grid zones
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Linked Tables
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Tables Edit, Join and Link
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Relationships in Linking and Joining Tables
Source Table (new information to be added)
Destination Table (existing information)
Many to one relation
Primary Key field (each record must have a
unique value)
Relate field (can have one or many records for
each value)
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Concept Summary

• Grid or raster representation is used to link
  hydrologic processes at the element or cell
  level
• Grid data model is based on square cells
• Point, line, area and network features have a
  corresponding grid cell representation which
  forms the basis of the raster-vector data model

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Concept Summary

• Features have descriptive attributes stored in an
  attribute table
• Attribute tables can be linked or joined to
  related tables using a key field

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Break Time
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Geodesy and Map Projections

• 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

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Types of Coordinate Systems

• (1) Global Cartesian coordinates (x,y,z) for the
  whole earth
• (2) Geographic coordinates (f, l, z)
• (3) Projected coordinates (x, y, z) on a local
  area of the earths surface
• The z-coordinate in (1) and (3) is defined
  geometrically in (2) the z-coordinate is defined
  gravitationally

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Global Cartesian Coordinates (x,y,z)
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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

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Origin of Geographic Coordinates
Equator
(0,0)
Prime Meridian
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Latitude and Longitude
Longitude line (Meridian)
N
W
E
S
Range 180ºW - 0º - 180ºE
Latitude line (Parallel)
N
W
E
S
(0ºN, 0ºE) Equator, Prime Meridian
Range 90ºS - 0º - 90ºN
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Latitude and Longitude in North America
60 N
30 N
60 W
120 W
90 W
0 N
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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
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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

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Ellipsoid or SpheroidRotate an ellipse around an
axis
Z
b
a
O
Y
a
X
Rotational axis
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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

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Representations of the Earth
Mean Sea Level is a surface of constant
gravitational potential called the Geoid
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Geoid and Ellipsoid
Earth surface
Ellipsoid
Ocean
Geoid
Gravity Anomaly
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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

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

• 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

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Map Projection
Flat Map Cartesian coordinates x,y (Easting
Northing)
Curved Earth Geographic coordinates f,
l (Latitude Longitude)
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Earth to Globe to Map
Map Projection
Map Scale
Scale Factor
Map distanceGlobe distance

(e.g. 0.9996)
(e.g. 124,000)
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Geographic and Projected Coordinates
(f, l)
(x, y)
Map Projection
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Projection onto a Flat Surface(Three Broad
Classes by Light Source)
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Gnomonic Projection
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Stereographic Projection
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Orthographic Projection
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World from Space Orthographic Projection
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Types of Projections

• Conic (Albers Equal Area, Lambert Conformal
  Conic) - good for East-West land areas
• Cylindrical (Transverse Mercator) - good for
  North-South land areas
• Azimuthal (Lambert Azimuthal Equal Area) - good
  for global views

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Conic Projections(Albers, Lambert)
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Azimuthal (Lambert)
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Projections Preserve Some Earth Properties

• Area - correct earth surface area (Albers Equal
  Area) important for mass balances
• Shape - local angles are shown correctly (Lambert
  Conformal Conic)
• Direction - all directions are shown correctly
  relative to the center (Lambert Azimuthal Equal
  Area)
• Distance - preserved along particular lines
• Some projections preserve two properties

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Geodesy and Map Projections

• 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

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Coordinate Systems

• Hydrologic calculations are done in Cartesian or
  Planar coordinates (x,y,z)
• Earth locations are measured in Geographic
  coordinates of latitude and longitude (f,l)
• Map Projections transform (f,l) (x,y)

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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)
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Universal Transverse Mercator Coordinate System

• 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) false easting and northing so
  you never have a negative coordinate

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Cylindrical Projections(Mercator)
Transverse
Oblique
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Mercator Projection
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UTM Projection (Zone 15)
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UTM Zone 14
-99
-102
-96
6
Origin
Equator
-120
-90
-60
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Universal Transverse Mercator Projection
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Summary Concepts

• Two basic locational systems geometric or
  Cartesian (x, y, z) and geographic or
  gravitational (f, l, z)
• Mean sea level surface or geoid is approximated
  by an ellipsoid to define an earth datum which
  gives (f, l) and distance above geoid gives (z)

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Summary Concepts (Cont.)

• To prepare a map, the earth is first reduced to a
  globe and then projected onto a flat surface
• Three basic types of map projections conic,
  cylindrical and azimuthal
• A particular projection is defined by a datum, a
  projection type and a set of projection
  parameters

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Summary Concepts (Cont.)

• Standard coordinate systems use particular
  projections over zones of the earths surface
• Types of standard coordinate systems UTM, State
  Plane, Texas State Mapping System, Standard
  Hydrologic Grid

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What is ArcView?

• Desktop geographic information system (GIS) from
  ESRI
• Uses scripting language called Avenue
• Customize GUI
• April 20, 2002 ArcGIS released

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Geographic Features
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Feature Attributes
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Feature Attributes
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Feature Attributes
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Sample Applications
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Site Selection Example

• At least five acres in size
• Vacant or for sale
• Zoned commercial
• Not subject to flooding
• Located not more than one mile from a heavy duty
  road
• Situated on terrain whose maximum slope is less
  than ten percent

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Parcel gt 5 Acre
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Parcels Zoned for Commercial
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Within Distance x of Highway
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Trinity River Basin
Continuous Space Representation
Discrete Space Representation
Digital Elevation Model (30m cells)
River reaches and their watersheds
TNRCC water quality segments and their
watersheds
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Soil Map of TNRCC Management Segment 841 Lower
West Fork Trinity River
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Watershed
Lumped Models
? Discrete flow systems e.g. watersheds,
streams ? Ordinary differential equations ?
Spatially averaged properties ? Network of
connected flow systems
Input, I(t)
A
A
1
2
A
Storage, S
1
A
C
2
Output, Q(t)
1
S
C
1
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30m DEM of Lower West Fork, Trinity River
Both regions and features can be represented
using elements
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Distributed Models
? Continuous flow systems e.g. groundwater,
air ? Spatially distributed properties ?
Vertically averaged or integrated flows ? Partial
differential equations ? Must solve both the
continuity and momentum equations
y
x