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GIS (GEOGRAPHIC INFORMATION

SYSTEMS)

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1. DEFINITION

SYSTEM

Any organised assembly of resources and procedures united and regulated by interaction or interdependence to complete a set of specific functions. Examples of systems are the solar system, information system. Your school can also be an example of a system. It is the assembly of teachers, students, syllabus and procedures united and regulated by the school constitution/ code of conduct to complete a set of specific functions, one of them being to produce good students.

Information systems

A system, whether automated or manual, that comprises of people, machines, and/or methods organised to collect, process, transmit, and disseminate data that represent user information.

What is GIS?

GIS stands for geographic information systems. Simply put, a GIS combines

layers of information about a place to give

you a better understanding of that place.

What layers of information you

combine depends on your purpose e.g.

finding the best location for a new

store, analyzing environmental damage,

viewing similar crimes in a city to detect

a pattern, and so on.

A full GIS, or geographic information system, requires:

Hardware (computers and peripherals)

Software

Data

People

and sound analysis methods for interpreting the results generated by the GIS.

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GIS software provides the functions and tools needed to store, analyze, and display information about places. The key components of GIS software are

Tools for entering and manipulating geographic information such as addresses or political boundaries

A database management system (DBMS)

Tools that create intelligent digital maps you can analyze, query for more information, or print for presentation

An easy-to-use graphical user interface (GUI)

GIS software ranges from low-end business-mapping

software appropriate for displaying sales territories to

high-end software capable of managing and studying large

protected natural areas.

GIS then can be defined as a “collection of computer hardware, software, geographic data and personnel designed to efficiently capture, store, update, manipulate, analyse and display all forms of geographically referenced data” (ESRI, 2002).GIS is a management tool that improves and enhances the decision making process. GIS does not make decisions. Better information leads to better decisions.

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2. COMPONENTS OF GIS

For a GIS to work, geographical data needs to be entered into the computer, stored in files or databases, manipulated using functions and presented in the form of maps, tables and graphs for decision makers.

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DATA ACQUISITION

Data Acquisition - is a process of identifying and collecting specific information (data) to solve a particular problem. Data acquisition focuses on collecting data with the correct amount of detail. Too much detail and complicated data for a project will take longer to process and will be more expensive. Data that is too simple or inaccurate will also slow the process down. The higher the accuracy of the data, the higher the cost of that data will be.

Objectives of Data Acqusition Data collection is a project on its own it is time consuming. The data collector must ensure that he / she has all the required and correct data for the project.

It involves various stages which are: Planning

Pre processing

Processing

Evaluation

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Planning- involves establishing user requirements, listing the data required and identifying sources of data.

Pre processing –involves obtaining data, digitising, image rectification, editing scanned map (images), correcting errors and improving quality

Processing - involves removing unwanted information and transformation i.e.integration of information and editing Vector Maps Evaluation – is the process of evaluating the project successes and failures Sources of Data Collection There are many sources and types of geographic data and proper research must be done to find the required data. Examples include: censuses, market research, questionnaires, field observation, field surveys, maps, aerial photographs, satellite remote sensing, GPS (Global Positioning System) is a instrument that uses satellites, to determine locations on the earth’s surface. The GPS provides precise time and position and information which enables GPS receiver to compute the distance of objects. The position is determined by measuring the distance from a group of satellites in space. Data Acquisition (information gathering) is a process that can be achieved in one or two forms: Primary Data Capturing - creating 'new' data

Secondary Data Capturing - gathering data that was collected by someone else (probably for a different purpose).

All data collected needs to be converted into digital (numerical) form before the GIS can make use of it. This can be done in two ways, namely Vector or Rasta form. Procedures such as digitising and scanning are involved in the conversion process. VECTOR:

Storing point, lines and polygons

Combination of x,y coordinates

Used for Discrete data RASTER:

Represented by grid cells (pixels)

Does not represent individual features

Used for continuous data

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Digital Spatial Data

• Raster

• Vector

• Real World

This is an illustration of transferring a real world geographic area into the raster and vector formats. In the raster format the geographic area is parcelled into numerous grid squares. In the vector format all entities are classified into points, lines or polygons.

Raster and Vector Data

Models

Vector Representation

X-AXIS

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600500400300200100

Y-AXIS

River

House

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Trees

Trees

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R

R R

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R T

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H

R

R

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G G

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Raster Representation

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Real World

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Raster data capture The most popular form of primary raster data capture is Remote Sensing.

Remote sensing – The collection of information about an object or event

without being in physical contact with the object or event. The most commonly

used application of remote sensing is the Satellite-borne instruments and

aerial photography to gather information, determine the location and amount

of resources on the surface of the Earth.

Remote sensing gives information about ground conditions over large areas

varying from relatively low cost to most expensive for example satellite

images. Remote sensing is sometimes referred to G.I.S. (Global imaging

systems).

Benefits of Remotely Sensed Data from satellites

Continuous acquisition of data

Regular revisit capacities (resulting in up to date information)

Broad regional coverage

Good resolution

Good spatial resolution

Ability to manipulate / enhance digital data

Ability to combine satellite digital data with other digital data

Cost effective data

Large archive of historical data

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Vector data capture

Vector Data is Layered

Spatial Data Analysis

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••

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••

••

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•

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1

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7 6

Lake

Features:

LinePoints:

ConnectedDetached

AreaText

•Lake

Geographic data are separated

into themes, tiled for speed of

access and placed on CD-ROM Network Analysis

30 30’ N

040 40’ E30 30’ N

040 50’ E

Structure of Vector Data

• There is a certain amount of relationship between vector data types. Sort of an inheritance, as each data type is often dependent upon one another. When representing geographic data in vector format, data is typically stored as:

• Points: points are zero dimensional objects, and represent geographic features such as wells, sample locations, or trees.

• Lines: lines represent one dimensional objects, or linear features, such as road and stream centerlines. Lines are made up of a series of interconnected points. A line typically starts and ends with a special point called a node, and the points that make up the rest of a line are called vertices.

• Polygons: polygons represent two dimensional objects such as the boundaries of a field, or property, or the outline of a building or lake. Polygons are made up of a series of connected lines where the starting point of a polygon is the same as the ending point.

Point

Line

Polygon

Vector is the major source of geographic data.

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Secondary Geographic Data Capture Raster Data Capture The most commonly used method for capturing data is by Scanning

Scanner – is an instrument used to converts images such as maps, photographs or page text into a digital form – so they can be stored and manipulated on computers. (Scanned maps and documents are used extensively in GIS as background maps and data stores)

Vector Data Capture Secondary data capture involves digitising maps and other geographic data sources.

Digitizing a method of data capturing that involves conversion of data in form, such as maps and aerial photographs, into digital form that is readable by a computer. This process involves assigning latitude and longitude coordinates. One of the disadvantages of digitising is it is labour intense

Photogrammetry a process of making maps using aerial photographs, this process involves obtaining measurements from photographs to produce maps of the Earth's surface and of features of the built environment.

Vector data is often overlaid on raster data for display and map production

Advantages of using Secondary Data

As secondary data is usually available more cheaply. The collection of secondary data is generally significantly quicker and easier (and hence less costly) than collecting the same data 'from scratch'

Existing data are likely to be available in more convenient form, digital format example internet.

Using secondary data can give us access to otherwise-unavailable organisations, individuals or locations.

Secondary data allows the researcher to compare data on 'time base' i.e. origin of data to current data.

Secondary data is likely to be pre-processed thus eliminating the time-consuming (and hence costly) analysis stage.

Disadvantages of using secondary data are as follow:

The method used to collect secondary data is often unknown to the user of the data (apart from major sources like Census).

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The user has little or no knowledge of the processing methods used.

The user rarely has access to the primary data to check against.

The researcher is forced to rely on the skills of the collector who collected and analysed the primary data, this is usually not a safe proposition.

One needs to do careful analysis of the strengths and weaknesses of particular

dataset. If datasets are in different formats one needs to consider the

following: costs, time spent on conversion

Checking the Quality of the Data

It is very important to consider the following;

How old is the data?

Where did it come from?

How accurate are the positional features?

Relevance of data to the project at hand?

The format is which the data kept?

Why was the data compiled?

Data Management

A database can be thought of an integrated set of data on a particular

subject. Geographic databases are simply databases that contain geographic data for

particular area and subject.

A geographic database is a critical part of an operational GIS.

Databases have the following advantages over the traditional way of filling: o Single location of data reduces redundancy and duplication. o Low cost maintenance. o Security and standards of data can be established and enforced.

What is a Database? A collection of information organised in such a way that a computer program can quickly select desired pieces of data. You can think of a database as an electronic filing system.

Traditional databases are organised by fields, records, and files.

A field or column is a single piece of information;

A record is a data entry; and

A file is a collection of records.

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For example: A telephone book is a database. It contains a list of records, each of which consists of three fields: name, address, and telephone number. A database holds all of the information about a record. The name, address, phone number, meeting attendance, publications ordered, committee membership, and any other information you choose is kept in a single database.

2. The Importance of Geographic Database

Managing Geographical Information is crucial.

A database allows you to manage and use an incredible variety of information easily.

Databases are easy to set-up, easy to manipulate and easy to use.

A database allows you to maintain order in what could be a very chaotic environment.

4. Database Security

Main functions of Database security are as follows:

Protecting the database from unauthorised users.

Ensures that users are allowed to do the things they are supposed to do.

Conducting backup, thus by recording the information and stored somewhere safe, i.e. if the computer room happens to burn down, or stolen.

DATA MANIPULATION:

It is a process that allows the user to work with GIS data to obtain the required

information. Data manipulation allows you to change (converting or

rearranging)the original spatial data in the GIS so that you can find the answers

you need. GIS systems also provide the tools to display and analyse

information. This is spatial analysis.

Data and Spatial Analysis

1. What is Spatial Analysis?

Spatial Analysis is the process of extracting or creating new information about a set of geographic features and examining the relationships between them.

Spatial analysis is the process by which we turn raw data into useful information. Effective spatial analysis requires an intelligent user, not just a

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powerful computer. Spatial analysis helps us in situations when our eyes might otherwise deceive us.

2. Querying information

Often, just looking at a map is not enough; you must also query it according to feature locations and attributes to solve problems.

You can begin to discover new spatial relationships when you start asking questions such as:

Where is...? Where’s the closest?

What’s inside?

And what intersects?

3. Buffering

Buffering is one of the important transformations available in GIS.

Given any object (that is point, line, or areas), a buffer operation builds new objects by identifying all areas that are within a certain specified distance of the original objects.

Figures below shows the instances of points, lines, and areas and the results of buffering.

Figure a: Buffer of five (5) Kilometres drawn around a line (e.g. a River).

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Figure b: Buffer of five (3) Kilometres drawn around a point (e.g a School).

Practical Case Studies of Spatial Analysis

Case studies

A logging company wishes to clearcut an area, but is required to avoid cutting in areas within 100m of streams – the company could build buffers 100m wide around all streams to identify these protected riparian areas.

A retailer is considering developing a new store on site, of a type that is able to draw consumers from up to 4 km away from its stores – the retailer could build a buffer around the site to identify the number of consumers living within 4 km of the site, in order to estimate the new store’s pontetial sales.

PRODUCT GENERATION

It involves data output that allows the user to generate the information required in

a variety of forms such as graphs, maps , tables, and reports.

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DEFINITIONS

Geographical Database: A collection of information about spatial locations and shapes of geographical features recorded, stored and organised in such a way that a computer program can quickly select desired pieces of data. A database can be thought of as an electronic filing system.

Spatial data Data that occupies mappable space and usually has a specific location according to some geo-referenced system such as latitude or longitude. Attribute data Data or information describing geographical characteristics of features or information that can be linked to spatial data. Primay data Data obtained for the first time and used specifically for the particular problem or issue being studied. First hand information collected from fieldwork, observations, questionnaires, interviews, surveys, etc., or collected directly from source. Secondary data: Second-hand or published information. Can be obtained from census data, reports, newspapers, internet, maps, statistics, etc. Geo referencing: The process of linking phenomena such as points, lines and areas to their location on the earth’s surface. It involves converting a place to X and Y coordinates so that it can accurately be plotted on a map.

Remote sensing: The process of obtaining information about land, water or an object, without physical contact between sensor and subject. Remote sensing often refers to collecting data using instruments aboard aircraft or satellites. Researchers use remote sensing systems to study the earth's resources and environment and to explore other planets. Sensor systems that take photographs with cameras record light or reflected energy in the visible spectrum.

Pixle: The smallest unit of spatial and spectral information represented in a digital image. It is a short form of the term “picture element”.

Resolution: Amount of detail with which a map depicts the location and shape of geographical features. The larger the map scale, the higher the possible spatial resolution. The area shown is smaller, hence more detail will be shown.

Pixle Resolution: An area represented by each cell or grid in a raster. The detail of the raster data depends on the size of the grid cells. A high pixle resolution means that a smaller area is depicted and more detail is shown. A low pixle resolution: A larger area shown and less detail.

Spectral resolution: The ability of a sensing system such as a satellite to

differentiate between electromagnetic radiation of different wavelengths. It also

refers to the range of wavelengths seen by a particular sensor.

Spatial Analysis

Spatial Analysis is the process of extracting or creating new information about a set of geographic features and examining the relationships between them.

Spatial analysis is the process by which we turn raw data into useful information.

Buffering Creating a zone within a pre-determined distance.

Buffering is one of the important transformations available in GIS.

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Given any object (that is point, line, or areas), a buffer operation builds new objects by identifying all areas that are within a certain specified distance of the original objects.

Data manipulation: the process used to organise data for your specific needs. Changes that one makes to the data during analysis. It involves converting, re-arranging, and analysing data to get answers.

Pre-processing: The process of correcting errors in the data and removing irrelevant information. It also involves ensuring that all data is projected the same way and is in the format required by the software being used.

Data management: Systematic and logical organisation of data. It makes it possible to protect data (data security), allows for data sharing and for the maintenance of data quality (keeping data in a reliable and usable condition) as well as having a backup system.

Data quality: The degree to which spatial information which has been captured satisfies the stated needs.

WORKSHEET

In groups, answer the following:

1. Geographical Information Systems (GIS) can store, manage, analyse and display data. To manage

the data in GIS you must look at the different parts that make up the system. Name any TWO parts

of GIS that make up the system.

1.1 _________________________________________________________________________

1.2____________________________________________________________________________

2. There are two types of data, namely spatial data and attribute data. Differentiate between spatial

data and attribute data.

Spatial data:______________________________________________________________________

_____________________________________________________________________________

__________________________________________________________________________

Attribute data:______________________________________________________________________

__________________________________________________________________________________

_________________________________________________________________________________

3. State whether the following types of spatial data are vector, raster or image data.

3.1

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_________________________________________________________________________________

3.2

________________________________________________________________________________

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4. From the list below identify examples of remotely sensed data and give reasons for your answer.

Type of data Remotely sensed data Reason

Yes NO

1. Topographical maps

2. Number of students in class

3. Weather forecast data

4. Rock types

5. Aerial photographs

6. Personal photograph

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