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Understanding Geographic Information System GIS
Content 1. Definitions of GIS & Brief Topic Explanations 2. Characteristics of GIS 3. a. Data 4. 1. Spatial Data 5. 2. Attribute Data 6. 3. Data Layers 7. 4. Layer Types 8. 5. Topology 9. b. Users / System 10. 1. Data Input 11. 2. Data Management 12. 3. Data Analysis 13. 4. Data Output 14. c. Software / Hardware
What do we know about GIS? u G eographic Maps u I nformation Data u S ystem Computerized Survey Measurements Tabular Data (Attributes)
What do we know about maps? Types of Maps (Familiar Examples) Street Maps u Infrastructure System Maps u Orthophotography u Contour Maps u
What do we know about maps? Information on a Typical Map Location of an Object u Information About an Object u
What do we know about maps? Problems Using Paper Maps Objects Can be Off the Map u Information Can be Missing or Out of Date u What You See is What You Get (Static) u
What Can GIS Do?
GIS Makes Static Maps Dynamic Move Around Using pan/zoom/jump u Change Symbology u Show Multiple Information Sets u Turn Information Sets on/off u
What is a GIS ? u u u A geographic information system (GIS) is a computer-based tool for mapping and analysing things that exist and events that happen on Earth. GIS technology integrates common database operations such as query and statistical analysis with the unique visualisation and geographic analysis benefits offered by maps. These abilities distinguish GIS from other information systems and make it valuable to a wide range of public and private enterprises for explaining events, predicting outcomes, and planning strategies.
Defining Geographic Information Systems GIS ‘A GIS is designed for the collection, storage, and analysis of objects and phenomena where geographic location is an important characteristic or critical to the analysis. ’ Stanley Aronoff “Computer tool for managing geographic feature location data and data related to those features. ” Allan B. Cox GIS is a tool for managing data about where features are (geographic coordinate data) and what they are like (attribute data), and for providing the ability to query, manipulate, and analyze those data.
Components of a GIS l A working GIS integrates these key components: – – – hardware software data people methods
H a r d w a r e l Hardware is the computer on which a GIS operates, including the resources available to the computer: – – – – l printers plotters digitizers scanners monitors network wide area communications Today, GIS software runs on a wide range of hardware types, from centralized computer servers to desktop computers used in stand-alone or networked configurations.
S o f t w a r e l GIS software provides the functions and tools needed to – – – store query display analyze create modify data.
S o f t w a r e (2) l Key software components are – – – tools for the input, manipulation, and output of geographic data a database management system (DBMS) tools for geographic query, analysis, and visualization a graphical user interface (GUI) for easy access to tools to document data sources and quality (metadata)
D a t a l Possibly the most important component of a GIS is the data. Geographic data and related tabular data can be collected in-house or purchased from a commercial data provider. A GIS will integrate spatial data with other data resources and can even use a DBMS, used by most organizations to organize and maintain their data, to manage spatial data.
P e o p l e l GIS technology is of limited value without the people who manage the system and develop plans for applying it to real world problems. GIS users range from technical specialists who design and maintain the system to those who use it to help them perform their everyday work.
M e t h o d s l A successful GIS operates according to a welldesigned plan and business rules, which are the models and operating practices unique to each organization.
GIS Tasks l General purpose GISs essentially perform five processes or tasks. – – – Input Manipulation Management Query and Analysis Visualization
How GIS works l A GIS stores information about the world as a collection of thematic layers that can be linked together by geography. This simple but powerful and versatile concept has proven invaluable for solving many real-world problems from tracking delivery vehicles, to recording details of planning applications, to modeling global atmospheric circulation.
As a concept they are similar to an overhead projector, with a series of transparencies laid upon it.
Conceptual Model of GIS “themes, ” “layers, ” or “coverages” The real world
I n p u t l l l Before geographic data can be used in a GIS, the data must be converted into a suitable digital format. The process of converting data from paper maps into computer files is called digitizing. Modern GIS technology has the capability to automate this process fully for large projects using scanning technology; smaller jobs may require some manual digitizing (using a digitizing table). Today many types of geographic data already exist in GIScompatible formats. These data can be obtained from data suppliers and loaded directly into a GIS.
Data Input The creation of digital spatial data. X & Y Coordinate: Used when a user has spatial data in X & Y coordinates. Database Entry: Commonly used when a user has attribute information related to common spatial locations, such as the census. Digitize: Used when a user has a paper map that they would like to convert into a digital file. Scan: Used when a user has a paper map that lends itself to reading spatial features in a rasterized format.
M a n i p u l a t i o n l It is likely that data types required for a particular GIS project will need to be transformed or manipulated in some way to make them compatible with your system. – l For example, geographic information is available at different scales (street centerline files might be available at a scale of 1: 100, 000; census boundaries at 1: 50, 000; and postal codes at 1: 10, 000). Before this information can be integrated, it must be transformed to the same scale. This could be a temporary transformation for display purposes or a permanent one required for analysis. GIS technology offers many tools for manipulating spatial data and for weeding out unnecessary data.
M a n a g e m e n t l l l For small GIS projects it may be sufficient to store geographic information as simple files. It is best to use a database management system (DBMS) to help store, organize, and manage data. A DBMS is nothing more than computer software for managing a database--an integrated collection of data.
Relational DBMSs l l l Data are stored conceptually as a collection of tables. Common fields in different tables are used to link them together. This simple design has been widely used because of its flexibility and wide deployment in many applications.
Retrieval Allows a GIS user to reproduce existing information from a database by browsing through the data or windowing the database.
Q u e r y a n d A n a l y s i s l Once you have a functioning GIS containing your geographic information, you can begin to ask simple questions such as – – – l Where is there stressed vegetation? How far is it between a contaminant source and a potentially exposed individual? Where is land zoned for industrial use? And analytical questions such as – – – Where all the residences that could be exposed to this facility’s air emissions? What is the dominant soil type for oak forest? If I build a new highway here, how will traffic be affected?
A Core Benefit l GIS provides both simple point-and-click query capabilities and sophisticated analysis tools to provide timely information to managers and analysts alike. GIS technology really comes into its own when used to analyze geographic data to look for patterns and trends, and to undertake "what if" scenarios. Modern GISs have many powerful analytical tools, but two are especially important: – Proximity analysis – Overlay analysis
Proximity Analysis l Typical questions: – – l How many low income households houses lie within two miles of this proposed incinerator site? What is the total number of soil samples within 50 feet of this pipeline? What proportion of the alfalfa crop is within 500 m of the well? How much of the site is within 100 feet of environmental contamination? To answer such questions, GIS technology uses a process called buffering to determine the proximity relationship between features.
Buffering Lines The blue band is a 60 m buffer around the road
Buffering Points The blue “balloon” is a buffer around the PCB hits (red points). It helps solve the problem of where to sample.
Buffer Generation Creates new polygons by expanding or shrinking existing polygons or by creating polygons from points.
Overlay Analysis l The integration of different data layers involves a process called overlay. At its simplest, this could be a visual operation, but analytical operations require one or more data layers to be joined physically. This overlay, or spatial join, can integrate data on soils, slope, and vegetation, or land ownership with tax assessment.
Overlay Analysis—Finding Regions The overlay of the buffer with the parcels solves the problem
Polygon Overlay and Dissolve Used when comparing two or more data layers.
Overlay Analysis—Selecting Points Overlaying the buffer with a sitewide sampling grid determines where and how to sample
Network Analysis Are techniques for routing resources along a set of linked linear features. Optimal path routing predicts the best route between two or more points based on distance, time, effort, or another measure. Often used for emergency response systems.
V i s u a l i z a t i o n l For many types of geographic operation the end result is best visualized as a map or graph. Maps are very efficient at storing and communicating geographic information. While cartographers have created maps for millennia, GIS provides new and exciting tools to extend the art and science of cartography. Map displays can be integrated with reports, threedimensional views, photographic images, and other output, such as multimedia.
Geographic Information System Data Spatial Data Represents features that have a known location on earth. Attribute Data The information linked to the geographic features (spatial data) that describe those features. Data Layers Are the result of combining spatial and attribute data. Essentially adding the attribute database to the spatial location. Layer Types A layer type refers to the way spatial and attribute information are connected. There are two major layer types, vector and raster. Topology How geographic features are related to one another and where they are in relation to one another.
Spatial Data Spatial or coordinate data represents features that have a known location on the earth. Points: X & Y Locations Line: Connected X & Y Locations Polygon: Connected X & Y Locations that contain attribute information. Raster: Row and column matrix represent geographic space.
Attribute Data Attribute data are the information linked to the geographic features (spatial data) that describe features. That is, attribute data are the “[n]ongraphic information associated with a point, line, or area elements in a GIS. ” O OO 2 1 1 1 1 OO 2 1 11 1 O 1 0 : WATER 1 : HIGHLAND 2 : WETLAND
Data Layers Are the result of combining spatial and attribute data. Essentially adding the attribute database to the spatial location.
Layer Types A layer type refers to the way spatial and attribute information are connected. There are two major layer types, vector and raster. Vector: Points, lines and polygons (spatial data) associated with databases of attributes (attribute data) are considered vector layer types. O 2 O 0 O 2 1 1 1 OO 2 1 11 1 1 O 1 Raster: A row and column matrix (pixels) of X & Y space with attribute information associated with each pixel is considered a raster layer type. O OO 2 1 1 1 0 : WATER 1 OO 2 1 11 1 O 1 1 : HIGHLAND 2 : WETLAND
Topology is the “way in which geographical elements are linked together”. Topology is how geographic features are related to one another and where they are in relation to one another. Topology is the critical element that distinguishes a GIS from a graphics or automated cartography system. It is essential to the ability of a GIS to employ spatial relationships. Topology is what enables a GIS to emulate our human ability to discern and manipulate geographic relationships. A B C D Parcel B is surrounded by Parcel A and Parcel C
Software / Hardware GIS software programs are usually either vector or raster based with capabilities in using both layer types. Vector Based Software • Arc. View • Arc. Map • Map. Info Raster Based Software • Erdas Imagine • IDRISI
Conclusions l l l GIS is rapidly becoming a key technology to support decision making at all scales The near future will continue to see accelerating growth in data availability and computing power to support GIS The strategic decision to make now is not whether, but when and how to use GIS to support environmental studies and decisions