IS 466 ADVANCED TOPICS IN INFORMATION SYSTEMS LECTURER : NOUF ALMUJALLY 14 – 11 – 2011 College Of Computer Science and Information, Information Systems.

IS 466 ADVANCED TOPICS IN INFORMATION SYSTEMS

LECTURER : NOUF ALMUJALLY

14 – 11 – 2011

College Of Computer Science and Information, Information Systems Department

2Introduction to Geographic Information Systems (GIS)

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Objectives

• GIS overview• GIS Functionality• GIS Components• GIS Data

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What is a GIS?

G : GeographicI : Information

S : System

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What is a GIS?

G, I, and S

G : geographic- Spatial data

I : Information- Databases- Representations

S : Systems- Users- Hardware- Software

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Where did GIS come from?

• GIS is built upon knowledge from geography, cartography, computer science, Information Systems, and Mathematics

• Geographic Information Science is a new interdisciplinary field built out of the use and theory of GIS

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Defining GIS

• Different definitions of a GIS have evolved in different areas and disciplines

• All GIS definitions recognize that spatial data are unique because they are linked to maps

• A GIS at least consists of a database, map information, and a computer-based link between them

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GIS Definition

• “A geographic information system is a computer-based information system that enables capture, modelling, storage, retrieval, sharing, manipulation, analysis, and presentation of geographically referenced data”

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Why does GIS Matter?

• GIS is a special class of information systems that keeps track not only of events, activities, and things, but also of where these events, activities, and things happen or exist

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Examples of geographical problems

• Government: where to locate public facilities (e.g. schools, hospitals and police stations)?

• Transportation: where to build the new highway that serves most critical bottleneck of the road network?

• Commercial: where to build new shops or good distribution centers that make most cost effective services?

• Travelers: where am I and how can I travel from Hong Kong International Airport to Hong Kong Baptist University?

• Country park management: where to locate hiking tracks that provide the best scenery for hikers at different levels with the minimum impact on the environment?

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Sources of Information on GIS

• The amount of information available about GIS can be Overwhelming

• Sources of GIS information include journals and magazines, books, professional societies, the World Wide Web, and conferences

• GIS has Web Home pages, network conference groups, professional organizations, and user groups

• Most colleges and universities now offer GIS classes in geography departments

12 GIS Components

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GIS Components

• There are four main components of a true GIS system (Marble 1990). These are:

1. Data input system• collects and/or processes spatial data from

existing sources, such as maps, remote sensing data, images, etc. Data can be "collected" through digitizing, scanning, interactive entry, etc.

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GIS Components

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GIS Components

2. computer hardware and software systems

• store the data, allow for data management and analysis, and can be used to display data manipulations on a computer monitor

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GIS Components

3. People • Specialist: includes programmers,

designers, developers• General Users: planners, scientists,

administrators • Viewers: everyone

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GIS Components

4. Output:• displays spatial database and analysis in

graphic (i.e., map) or tabular for

18 GIS Data

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GIS Data

• GIS involves two geographic data components:1. spatial data• the location and shape of geographic features

and their spatial relationships to other features

2. attribute data• Descriptive information about the geographic

features (the spatial feature)

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Con.

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The Geographic Database

22 1 -Spatial Data Model

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Spatial Data Models

• GIS uses two basic data models to represent spatial features:

• Vector• Raster

• The data model determines how the data are structured, stored, processed, and analyzed in a GIS

• Many GIS functions are either vector-based or raster-based.

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Vector and Raster Data Models

• The vector data model uses points and their x,

y coordinates to construct spatial features of

points, lines, and areas.

• The raster data model uses a grid to represent

the spatial variation of a feature. Each cell in the

grid has a value that corresponds to the

characteristic of the spatial feature at that

location.

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Vector vs. Raster Data Models

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Vector Data Models

• The vector data model consists of three types of geometric objects: point, line, and polygons.

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Vector Data Models - Points

• The vector data model consists of three types of geometric objects: point, line, and polygons.

1. Points• associated with single set of coordinates (X, Y)• Examples include street lights, wells,

telephone polls, buildings, trees.• Ex. The location of hospitals and clinics

for the country of Tunisia

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Vector Data Models - Lines

2. Lines• connected sequence of coordinate pairs• Lines have no width, but have a starting and

ending point (referred to as arcs in ArcGIS).• Examples include streets, sewer lines, railroad

tracks, rivers, flight paths.• Ex. streams (blue lines),

pipeline (green line), and fault

lines (brown) for a location

in New Mexico.

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Vector Data Models - Polygons

3. Polygons • sequence of interconnected lines whose 1st & last

coordinate points are the same• closed figures that encompass a homogeneous

area.• Examples include lakes, buildings, countries, states,

counties, individual territories.

• Ex, Three polygon layers:flood zones (dark blue),Schools (red) and city limits(light blue plus flood zones)for Redlands, California.

30 2 -Attribute Data Model

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Attribute Data Models

• Descriptors of geographic (spatial) data. Such data may be numbers or text (characters) and are generally stored in tabular format and linked to the spatial data by a common identifier

• Examples include owner's name for a building, tree height and species name for a tree location, etc.

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Attribute Data Models

• Attribute data are stored logically in flat files.

• A flat file is a matrix of numbers and values stored in rows and columns, like a spreadsheet.

• Both logical and physical data models have evolved over time.

• DBMSs use many different methods to store and manage flat files in physical files.

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Digitizing

• The process of representing an analogue signal or an image by a discrete set of its points is known as Digitizing.

• This data after conversion is in the binary format, which is directly readable by computer.

• The data to be converted can be a text, an image, audio or a video. 

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Types of Digitizing

1. Manual Digitizing: It is done using digitizing tablet. The operator manually traces all the lines from his hardcopy map and creates identical digital map on the computer. It is very time consuming and level of accuracy is also not very good.

2. Heads-up Digitizing: It is similar to manual digitizing in the way that lines have to be drawn manually but directly on the computer screen. So in this level of accuracy increases and time taken decreases.

3. Interactive tracing method: It is improvement over Heads-up digitizing in terms of speed and accuracy.

4. Automatic Digitizing: It is automated raster to vector conversion using image processing and pattern recognition techniques. In this technique computer traces all the lines, which results in high speed and accuracy along with improved quality of images.

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The Digitizer

• Device used for digitization is known as digitizer.• It is an electromagnetic device consisting of a table

upon which a map or a document to be scanned is placed.

• This device enters the spatial coordinates of mapped features from a map or a document to the computer.

• It is done with the help of a mouse or a hand held magnetic pen.

• The most commonly used digitizers are:• Electrical orthogonal fire wire grid digitizer.• Electrical wave phase type digitizer.

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Con.

• A device known as “puck’ is used in cases where high degree of precision is required.

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Questions a GIS can answer

A comprehensive GIS can answer all of the following

Questions

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Locations: What is at?

• Here we are seeking to find out what exists at particular location

• A location can be described in many different ways. For example, place name, zip code, or latitude and longitude coordinates.

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GIS generates information - locations

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Conditions: Where is it?

• Instead of identifying what exists at a given location, you want to find a location where certain conditions are satisfied.

• For example, you wish to find a house assessed at less than $200,000 with 4 bedrooms and made of wood or stucco

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GIS generates information - conditions

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Trends: What has changed since?…

• This seeks to discover the differences between an area as the result of the passing of time

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GIS generates information - trends

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Patterns: What a spatial patterns exist?

• This seeks to discover what types of patterns may exist in the newly created data file that were not visible before.

• For example you may wish to know where motor vehicle accidents occur and at what times

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GIS generates information - Patterns

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Modelling: What If … ?

• This seeks to determine what happens if something is changed within an area.

• For example a new subdivision is added to a school district, or a toxic substance seeps into the local ground water supply, or an earthquake of a given magnitude occurs at a given point, or you want to locate a new business

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GIS generates information - models

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Questions ??