Introduction to Geographic Information Systems and Sample Applications

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

What is GIS???? Standard definition: Sound efficient?????? 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??????

GIS: Simplified A computer-based tool for mapping and analyzing things. Geospatial Database: a set of compatible data layers or themes

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

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

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

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 Spatial data – Existing within space. In a GIS, spatial data are the geographic relationships between features based on their locations. Attributes, or attribute data - is descriptive information about features or elements of a database. A GIS stores attributes in tables and links them to the map features they describe. Attributes of a river might include its name, length, average depth, and so on.

Attributes GIS stores more than just maps Relationship between map features and attributes within a GIS Dynamic interactive maps In general, all map data is made up of point, line, and area features. Some combinations or special cases of these three types of features represent complex real-world objects. For example, a school could be represented by a combination of areas (buildings and playgrounds), lines (sidewalks and driveways), and points (individual trees and trash bins).

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). One of the primary capabilities of a GIS is data storage. The maps and other data you enter are stored in digital form. Imagine them as digital layers with their attributes attached

Database Management System DBMS Inside the DBMS, spatial data is stored as digital layers with their associated attributes

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 If you asked why spatial data should be stored in a GIS, a casual answer would be "so that it can be taken out again." If this were literally true, there may be no need for a GIS. Perhaps a filing cabinet would suffice. You can hang up the maps in a filing cabinet and be done with it. input, editing, and management of data; data query, analysis, and visualization; and output operations.

Discrete and Continuous Space Discrete Space: Vector GIS Lumped models Continuous Space: Raster GIS, Tin Distributed models

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 DRM Node Polygon - a closed set of lines

River Reaches Flow along lines through the landscape

River Basins Hydrologic features containing several different types of flow processes

Spatial Data: Grid (Raster) format Raster data are described by a cell grid, one value per cell: Number of rows Number of Columns (X,Y) Cell size NODATA cell

NEXRAD Rainfall Intensity Image October 18, 1994 @ 3:00 AM (CST)

NEXRAD Rainfall Intensity Image October 18, 1994 @ 4:00 AM (CST)

Raster and Vector Data Vector Raster Point Line Polygon Zone of cells DRM Zone of cells Polygon

Points as Cells

Line as a Sequence of Cells

Polygon as a Zone of Cells

Vector Data Uses positions to represent real world entities Points, lines, polygons Vector representation of a reservoir and highway. The small squares are nodes—point locations specified with latitude and longitude coordinates. Line segments connect nodes to form line features. In this case, the line feature colored red represents the highway. Series of line segments that begin and end at the same node form polygon features. In this case, two polygons (filled with blue) represent the reservoir. The vector data model is consistent with how surveyors measure locations at intervals as they follow a property boundary. Computer-aided drafting (CAD) software used by surveyors, engineers, and others, stores data in vector form. Reservoir and Highway

Raster Data Samples attributes at fixed intervals List of numbers, one number per cell The raster approach, by contrast, involves sampling attributes at fixed intervals. Each sample represents one cell in a checkerboard-shaped grid. The graphic above illustrates a raster representation of the same reservoir and highway. The area covered by the aerial photograph has been divided into a grid. Every grid cell that overlaps one of the two selected entities is encoded with an attribute that associates it with the entity it represents. Raster data consists of a list of numbers, one number for each grid cell, each number representing an entity. For example, grid cells that represent the highway might be represented with the number 1 and grid cells representing the reservoir might be coded with the number 2. Digital remote sensing systems, which are gradually replacing cameras as primary sources of geographic data, produce raster data by scanning the Earth’s surface pixel-by-pixel, one row at a time. The raster data model is a smart choice for representing phenomena that lack clear-cut boundaries, such as terrain elevation, vegetation, and precipitation. Reservoir and Highway

Hydrologic Cycle Atmospheric water Surface water Subsurface water Connecting processes in the hydrologic cycle involves linking spatial features of various kinds

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

Levels of Analysis: Relational Database Relational Linkages Spatial Attributes Water Right Locations Descriptive Attributes

Feature Attribute Table Fields Records

Value Attribute Table Attributes of grid zones

Linked Tables

Tables: Edit, Join and Link

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)

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

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

Break Time

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

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 earth’s surface The z-coordinate in (1) and (3) is defined geometrically; in (2) the z-coordinate is defined gravitationally

Global Cartesian Coordinates (x,y,z) Greenwich Meridian Equator •

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

Origin of Geographic Coordinates Equator (0,0) Prime Meridian

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

Latitude and Longitude in North America 120 W 60 W 90 W 0 N

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

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

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

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

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

Geoid and Ellipsoid Gravity Anomaly Earth surface Ellipsoid Ocean

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

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

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

Map Projection Flat Map Curved Earth Cartesian coordinates: x,y (Easting & Northing) Curved Earth Geographic coordinates: f, l (Latitude & Longitude) DRM

Earth to Globe to Map Map Projection: Map Scale: Scale Factor Representative Fraction Globe distance Earth distance = Scale Factor Map distance Globe distance = (e.g. 1:24,000) (e.g. 0.9996)

Geographic and Projected Coordinates (f, l) (x, y) Map Projection

Projection onto a Flat Surface (Three Broad Classes by Light Source)

Gnomonic Projection

Stereographic Projection

Orthographic Projection

World from Space – Orthographic Projection

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

Conic Projections (Albers, Lambert)

Azimuthal (Lambert)

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

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

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)

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 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

Cylindrical Projections (Mercator) Transverse Oblique

Mercator Projection

UTM Projection (Zone 15)

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

Universal Transverse Mercator Projection

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)

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

Summary Concepts (Cont.) Standard coordinate systems use particular projections over zones of the earth’s surface Types of standard coordinate systems: UTM, State Plane, Texas State Mapping System, Standard Hydrologic Grid

What is ArcView? Desktop geographic information system (GIS) from ESRI Uses scripting language called Avenue Customize GUI April 20, 2002 – ArcGIS released

Below is a typical ArcView project Below is a typical ArcView project. A map, chart, and table have been used to depict migration patterns in the United States. The ArcView interface consists of windows that present information in different ways. Rows of menus, buttons, and tools at the top of the main application window allow you to view and perform analytical operations on the data in the database. We’ll look at each thing individually.

Geographic Features Points, lines and polygons

Feature Attributes

Feature Attributes

Feature Attributes

Sample Applications

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

Parcel > 5 Acre

Parcels Zoned for Commercial

Within Distance ‘x’ of Highway

segments and their watersheds 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

Soil Map of TNRCC Management Segment 841 Lower West Fork Trinity River

Lumped Models  Discrete flow systems e.g. watersheds, streams  Ordinary differential equations  Spatially averaged properties  Network of connected flow systems dS dt = I - Q Input, I(t) A A A 1 2 Storage, S 1 A C Output, Q(t) 2 1 S C 1

30m DEM of Lower West Fork, Trinity River Both regions and features can be represented using elements

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