1.gis

www.mcsmapping.com August 25, 2010

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© Magendhiran Consultancy Services. All rights reserved. www.mcsmapping.com

GIS

Fundamentals

8/25/2010 1 © Magendhiran Consultancy Services. All rights reserved. www.mcsmapping.com

• History

• Definition

• Components

• Applications

• Data models

• Raster Data

• Vector Data

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Presentation Outline


• GIS is built upon knowledge from geography,

cartography, computer science and mathematics

• Geographic Information Science is a new

interdisciplinary field built out of the use and

theory of GIS

Where did GIS come from?


• GIS’s origins lie in thematic cartography (manual map overlay)

• Computer cartography advances in 1950s and 1960s

• Early influential data sets were the World Data Bank and the GBF/DIME files. Early systems were CGIS, MLMIS, GRID and LUNR

• The Harvard University ODYSSEY system was influential due to its topological arc-node (vector) data structure

• GIS was significantly altered by (1) the PC and (2) the workstation

• During the 1980s, new GIS software could better exploit more advanced hardware

• User Interface developments led to GIS's vastly improved ease of use during the 1990s

• During the 1980s, new GIS software could better exploit more advanced hardware

A Brief History of 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 (Space matters!)

• A GIS at least consists of a database, map information,

and a computer-based link between them

Defining GIS


Geographic Information Systems (GIS)

• The common ground between information processing and the many fields using spatial analysis techniques. (Tomlinson, 1972)

• A powerful set of tools for collecting, storing, retrieving, transforming, and displaying spatial data from the real world. (Burroughs, 1986)

• A computerized database management system for the capture, storage, retrieval, analysis and display of spatial data. (NCGIA, 1987)

• A decision support system involving the integration of spatially referenced data in a problem solving environment. (Cowen, 1988)

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An Inelegant Definition for GIS

A system of integrated computer-based tools for end-to-end processing (capture, storage, retrieval, analysis, display) of data using location on the earth’s surface for interrelation in support of operations management, decision making, and science.

• set of integrated tools for spatial analysis

• encompasses end-to-end processing of data(capture, storage, retrieval, analysis/ modification, display)

• uses explicit location on earth’s surface to relate data

• aimed at decision support, as well as on-going operations and scientific inquiry


GIS: intuitive description

• A map with a database behind it.

• A virtual representation of the real world and its infrastructure.

• A consistent “as-built” of the real world, natural and manmade

Which is

• queried to support on-going operations

• summarized to support strategic decision making and policy formulation

• analyzed to support scientific inquiry

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Why Study GIS?• 80% of local government activities estimated to be geographically based

– plats, zoning, public works (streets, water supply, sewers), garbage collection, land ownership and valuation

• a significant portion of state government has a geographical component

– natural resource management

– highways and transportation

• businesses use GIS for a very wide array of applications

– retail site selection & customer analysis

– logistics: vehicle tracking & routing

– natural resource exploration (petroleum, etc.)

– precision agriculture

– civil engineering and construction

• scientific research employs GIS

– geography, geology, botany

– anthropology, sociology, economics, political science

– Epidemiology, criminology


The major areas of GIS application• Local Government

– Public works/infrastructure management (roads, water, sewer)

– Planning and environmental management

– property records and appraisal

• Real Estate and Marketing-Retail site selection, site evaluation

• Public safety-Crime analysis, fire prevention, emergency management

• Natural resource exploration/extraction - Petroleum, minerals, quarrying

• Transportation- Airline route planning, transportation modeling

• Public health and epidemiology

• The Geospatial Industry - Data development, application development, programming

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1. The potential and substantial benefits of using GIS make it a very important tool making the work of any organization easier and more productive. Some of the potential benefits of GIS are:

2. Opportunity to reduce sets of manual maps held and associated storage costs.

3. Faster and more extensive access to geographic information.

4. Improved analysis e.g. Of areas, distances, patterns, etc.

5. Better communication of information to public officers, members.

6. Improved quality of services.

7. Better targeting and coordination of services.

8. Improved productivity in providing public information.

9. Improved efficiency in updating maps.

10. The ability to track and monitor growth and development over time

11. Improved ability to aggregate data for specific sub areas.

12. Thus GIS's have become indispensable tools for governance, commerce, and environmental and social science.

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Advantages of GIS


Examples of Applied GIS

• Urban Planning, Management & Policy– Zoning, subdivision planning– Land acquisition– Economic development– Code enforcement– Housing renovation programs– Emergency response– Crime analysis– Tax assessment

• Environmental Sciences– Monitoring environmental risk– Modeling storm water runoff– Management of watersheds, floodplains, wetlands, forests,

aquifers– Environmental Impact Analysis– Hazardous or toxic facility sites– Groundwater modeling and contamination tracking

• Political Science– Redistricting– Analysis of election results– Predictive modeling

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Examples of Applied GIS contd.

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•Civil Engineering/Utility•Locating underground facilities•Designing alignment for freeways, transit•Coordination of infrastructure maintenance

• Business•Demographic Analysis•Market Penetration/ Share Analysis•Site Selection

•Education Administration• Attendance Area Maintenance• Enrollment Projections• School Bus Routing

•Real Estate•Neighborhood land prices•Traffic Impact Analysis•Determination of Highest and Best Use

•Health Care•Epidemiology• Needs Analysis• Service Inventory

© Magendhiran Consultancy Services. All rights reserved. www.mcsmapping.com 8/25/2010 14

Components of GIS


GIS System Architecture and Components

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Transformation

and Analysis

Data Input

Query InputGeographic

Database

Output: Display

and Reporting


The GIS Data Model: Implementation

• Data is organized by layers, coverages or themes (synonomousconcepts), with each layer representing a common feature.

• Layers are integrated using explicit location on the earth’s surface, thus geographic location is the organizing principal.

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Digital Orthophoto

Streets

Hydrography

Parcels

Buildings

Zoning

Utilities

Administrative Boundaries


The GIS Model: example




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roads

hydrology

topography

longitude

longitude

longitude

Here we have three layers or themes:

--roads,

--hydrology (water),

--topography (land elevation)

They can be related because precise geographic

coordinates are recorded for each theme.

Layers are comprised of two data types

•Spatial data which describes location (where)

•Attribute data specifying what, how much, when

Layers may be represented in two ways:

•in vector format as points and lines

•in raster(or image) format as pixels

All geographic data has 4 properties:

projection, scale, accuracy and resolution


Spatial and Attribute Data

• Spatial data (where)

– specifies location

– stored in a shape file or similar geographic file

• Attribute (descriptive) data (what, how much, when)

– specifies characteristics at that location, natural or human-created

– stored in a data base table

• GIS systems traditionally maintain spatial and attribute data separately, then “join” them for display or analysis

– for example, in QGIS, the Attributes of … table is used to join a shapefile (spatial structure) with a data base table containing attribute information in order to display the attribute data spatially on a map

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Representing Data

Raster Model• area is covered by grid with (usually) equal-sized, square cells

• attributes are recorded by assigning each cell a single value based on the majority feature (attribute) in the cell, such as land use type.

• Image data is a special case of raster data in which the “attribute” is a reflectance value from the geomagnetic spectrum

– cells in image data often called pixels (picture elements)

Vector ModelThe fundamental concept of vector GIS is that all geographic features in the real

work can be represented either as:

• points or dots (nodes): trees, poles, fire plugs, airports, cities

• lines (arcs): streams, streets, sewers,

• areas (polygons): land parcels, cities, counties, forest, rock type

Because representation depends on shape, QGIS refers to files containing vector data as shapefiles

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0 1 2 3 4 5 6 7 8 90 R T1 R T2 H R3 R4 R R5 R6 R T T H7 R T T8 R9 R

Real World

Vector RepresentationRaster Representation

Concept of Vector and Raster

line

polygon

point


Advantages of raster data

1. Simple data structure

2. Easy and efficient overlaying

3. Compatible with RS imagery

4. High spatial variability is efficiently represented

5. Simple for own programming

6. Same grid cells for several attributes

Advantages of vector data

1. Compact data structure

2. Efficient for network analysis

3. Efficient projection transformation

4. Accurate map output.

Raster & Vector Data


The key properties of spatial data• Projection: the method by which the curved 3-D surface of the

earth is represented by X,Y coordinates on a 2-D flat map/screen

– distortion is inevitable

• Scale: the ratio of distance on a map to the equivalent distance on the ground

– in theory GIS is scale independent but in practice there is an implicit range of scales for data output in any project

• Accuracy: how well does the database info match the real world

– Positional: how close are features to their real world location?

– Consistency: do feature characteristics in database match those in real world -is a road in the database a road in the real world?

– Completeness: are all real world instances of features present in the database? - Are all roads included.

• Resolution: the size of the smallest feature able to be recognized– for raster data, it is the pixel size

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1.gis

Education

gis definitions

applied gis

brief history of gis

study gis

new gis software

spatial data

display of data

major areas of gis application