Understanding GeographicInformation System GIS

Content

1. Definitions of GIS & Brief Topic Explanations

2. Characteristics of GIS

a. Data

1. Spatial Data

2. Attribute Data

3. Data Layers

4. Layer Types

5. Topology

b. Users / System

1. Data Input

2. Data Management

3. Data Analysis

4. Data Output

c. Software / Hardware

What do we know about GIS?What do we know about GIS?

GG eographic eographic MapsMaps II nformation nformation DataData SS ystem ystem ComputerizedComputerized

Survey MeasurementsSurvey Measurements

Tabular DataTabular Data(Attributes)(Attributes)

Types of Maps (Familiar Examples)Types of Maps (Familiar Examples)

What do we know about maps?What do we know about maps?

Street MapsStreet Maps Infrastructure System MapsInfrastructure System Maps OrthophotographyOrthophotography Contour MapsContour Maps

Information on a Typical MapInformation on a Typical MapInformation on a Typical MapInformation on a Typical Map

What do we know about maps?What do we know about maps?

Location of an ObjectLocation of an Object Information About an ObjectInformation About an Object

Problems Using Paper MapsProblems Using Paper Maps

What do we know about maps?What do we know about maps?

Objects Can be Off the MapObjects Can be Off the Map Information Can be Missing or Out of Information Can be Missing or Out of

DateDate What You See is What You Get What You See is What You Get

(Static)(Static)

What Can GIS Do?What Can GIS Do?What Can GIS Do?What Can GIS Do?

GIS Makes Static MapsGIS Makes Static Maps

Move Around Using Move Around Using pan/zoom/jumppan/zoom/jump

Change SymbologyChange Symbology Show Multiple Information SetsShow Multiple Information Sets Turn Information Sets on/offTurn Information Sets on/off

DynamicDynamicDynamicDynamic

What is a GIS ?What is a GIS ?

A geographic information system (GIS) is a A geographic information system (GIS) is a computer-based tool for computer-based tool for mappingmapping and and analysinganalysing things that exist and events that happen on Earth.things that exist and events that happen on Earth.

GIS technology integrates common GIS technology integrates common databasedatabase operations such as query and operations such as query and statisticalstatistical analysis analysis with the unique with the unique visualisationvisualisation and and geographicgeographic analysis benefits offered by maps.analysis benefits offered by maps.

These abilities distinguish GIS from other These abilities distinguish GIS from other informationinformation systemssystems and make it valuable to a and make it valuable to a wide range of public and private enterprises for wide range of public and private enterprises for explaining events, predicting outcomes, and explaining events, predicting outcomes, and planning strategies.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

A working GIS integrates these key components:– hardware– software– data– people– methods

H a r d w a r e

Hardware is the computer on which a GIS operates, including the resources available to the computer:

– 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

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)

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– tools to document data sources and quality (metadata)

D a t a

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

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

A successful GIS operates according to a well-designed plan and business rules, which are the models and operating practices unique to each organization.

GIS Tasks

General purpose GISs essentially perform five processes or tasks.– Input– Manipulation– Management– Query and Analysis– Visualization

How GIS works

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

GIS “themes,” “layers,” or “coverages”

The real world

I n p u t

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 GIS-compatible formats. These data can be obtained from data suppliers and loaded directly into a GIS.

Data Input

X & Y Coordinate: Used when a user has spatial data in X & Y coordinates.

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.

The creation of digital spatial data.

Database Entry: Commonly used when a user has attribute information related to common spatial locations, such as the census.

M a n i p u l a t i o n

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.

– 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

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

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

Once you have a functioning GIS containing your geographic information, you can begin to ask simple questions such as

– 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 are 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

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

Typical questions:– 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 60m 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.

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Buffer Generation

Creates new polygons by expanding or shrinking existing polygons or by creating polygons from points.

Overlay Analysis

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

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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

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, three-dimensional views, photographic images, and other output, such as multimedia.

Topology

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.

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

Polygon: Connected X & Y Locations that contain attribute information.

Line: Connected X & Y Locations

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]on-graphic information associated with a point, line, or area elements in a GIS.”

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Data Layers

Are the result of combining spatial and attribute data. Essentially adding the attribute database to the spatial location.

Raster: A row and column matrix (pixels) of X & Y space with attribute information associated with each pixel is considered a raster layer type.

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.

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Topology

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.

B CA D Parcel B is surrounded byParcel A and Parcel C

Software / Hardware

Raster Based Software

Vector Based Software

GIS software programs are usually either vector orraster based with capabilities in using both layer types.

• ArcView

• ArcMap

• MapInfo

• Erdas Imagine

•IDRISI

Conclusions

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