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Friday, October 1, 2010

What is GIS?

Definition: A map is a graphic form, normally to scale, of spatial abstraction of features on, or in relation to, the surface of the Earth.

Types of maps

  1. Topographic maps
  2. Thematic maps

Topographic map:

A reference tool, showing the outlines of selected natural and man-made features of the Earth. „ "Topography" refers to the shape of the surface, represented by contours and/or shading, but topographic maps also show roads and other prominent features.

Thematic map:

A tool to communicate geographical concepts such as
  • The distribution of population densities, climate, movement of goods, land use etc.
  • Line maps versus photo (image) maps
„* 2D vs 3D maps

Characteristics of maps

  • Scale
  • Projection


The scale of a map is the ratio between distances on the map and corresponding distances in the real world, e.g., if a map has a scale of 1:50,000, then 1 cm on the map equals 50,000 cm or 0.5 km on the Earth's surface.
"Small scale" and "large scale" is often confused, e.g, 1:50,000 vs. 1:500,000
The scale controls not only how features are shown, but what features are shown, e.g., Engineering building: 0.2mm*50,000=10 m„ Map projections. The Earth's surface is curved but as it must be shown on a flat sheet, some distortion is inevitable.


A projection is a method by which the curved surface of the earth is represented on a flat surface.
Numerous projections have been invented for various applications
  • „ Cartographic abstraction „- Selection of the few features in the real world to include classification of selected features into groups (e.g., bridges, churches, railways)
  • Simplification of jagged lines (e.g., coastlines)
  • Exaggeration of features to be included that are to small to show at the scale of the map Symbolization to represent the different classes of features chosen

Geographic (Geo-spatial) information

  1. Information about places on the earth’s surface
  2. „ Knowledge about where something is
  3. Knowledge about what is at a given location
  4. Can be very detailed or very coarse
  5. Often relatively static
  6. „ Can be very voluminous

Basic Concept of a GIS

GIS can be considered as a map information system for management, analysis, presentation and distribution.the applicaion of GIS can be found "here".
Basic Concept of Geographic Information System

The Academic Definition
"A system of hardware, software, data, people, organizations and institutional arrangements for collecting, storing, analyzing, and disseminating information about areas of the earth." (Dueker & Kjerne, 1989)

Tao’s Definition
A GIS is a computer-based information system for collection, management, manipulation, analysis, presentation, and dissemination of geospatially referenced data.

A Mathematical Definition
  • Measure aspects of geographic phenomena and processes;
  • Represent these measurements in the form of a computer database;
  • Operate these representations to produce more measurements and
  • To discover new relationships;
  • Transform these representations to conform to other frameworks of entities and relationships.

GIS Workflow

Basic Concept of Geographic Information System GIS is a location based information system:
A GIS stores information about the world as a collection of layers that can be linked together by geography.
Why themes (layers)?
Modeling of actual features in GIS
Modeling of actual features in GIS
  • Logical breakdown of data - related objects in each theme
  • Assemble maps for different purposes by combining themes
  • Examine interaction between themes
  • Create new themes
Paper maps use symbolism to distinguish between layers, to compensate for the limitations of the technology

Alternative Names

  • Geospatial (Spatial) Information System
  • Geographic(al) Information System
  • Land Information System
  • Environmental Information System
  • Automated Mapping/Facilities Management
  • Geographical Information Sciences (GIScience)
  • Geographical Information Services (GIServices)
  • Desktop Mapping

Components of a GIS

Components required for full functionality of geographic Information System
Components required for full functionality of geographic Information System
  1. Hardware
  2. Software
  3. Data
  4. People
  5. Methods


  • Computers (PC, workstations, servers)
  • CPU, Pentium 4 2.5GHz ? Memory, 8GB
  • Storage devices (Mass storage)
  • Hard disks, Tape (4mm, 8mm 8GBs), Optical disks (>1GB, $100 per Disk), CD –ROM (640MB, $1-2 per CD)/DVD
  • Zip drivers (100-200MB, $20 per disk), Jazz-drivers (1G, $50 per disk), Flash cards, USB HD
Input devices
  • Keyboard, Scanner, Digitizer, Camera, Voice recognition
  • GPS, stereo plotter, remote sensing sensors
  • Output devices
  • Graphics monitors (graphics cards)
  • Printers (dot matrix/Laser/Inkjet)
  • Plotter (Drum/Flatbed)
  • Communication/networking devices
  • WAN/LAN/High-Speed Network
  • Modem/Phone Lines/Cable
As the Internet evolves, its data transfer rate is increasing very quickly. From the first level(CA-1, 10MB/s), to the second(CA-2, 150MB/s), to the third(CA-3, 10GB/s), and beyond.


  • Operating systems
  • Windows/UNIX/LINUX
  • Basic GIS software
  • ESRI: ArcGIS, ArcInfo, ArcView
  • Intergraph: Geomedia, MGE
  • Auto Desk: AutoCAD Map, MapGuide
  • MapInfo: MapInfo
  • Bently: Microstation
  • PCI Geomatica (PANMAP, SPANS)
  • Caris Data Base Management Systems (DBMS)
  • Oracle, DB2, Informix, Sybase, Microsoft SQL, Access
Development languages
  • Common programming languages: VC, VB, Java, Fortran
  • Micro Language: Does not exist anymore( e.g., Avenue: Arcview, MapBasics: Mapinfo, AML, MDL: Microstation)


  1. Spatial data e.g., Coordinates, location of a well, boundaries, road networks
  2. Non-spatial data (attributes, aspatial data) …e.g., Land ownership, address, population densities, soil PH values
  3. Data relationships (spatial relationship-topology, attribute relations)

    1. Temporal data
    2. Metadata (data about data)

Spatial data„ Objects or entities that are referenced by their location
  • Latitude / longitude coordinates …x / y coordinates
  • Street address
  • Administrative unit

Attribute data
  • Data that are linked to the spatial objects
  • Census data by administrative unit
  • Land parcel ownership records
  • Soil or vegetation characteristics
  • Health records by medical center
  • Road quality information

Data Relations Traditionally information is organized in lists, maps add information about the “where” of the data

Exploring Relationships
  • Based on geographic location and proximity, GIS makes connections between activities
  • Looking at data geographically can often suggest new insights,
  • These connections are often unrecognized without GIS, but can be vital to understanding and managing activities and resources e.g., we can link pollution sources with disease patterns


…GIS expertise and knowledge


  • Problem solving skills
  • Team skills
  • Communication skills
  • Management skills
Which is the most costly component in a GIS?
Functional Requirements for GIS
  • Data input
  • Existing maps, field observations, aerial photographs, sensors (airborne and satellites)
  • Data storage and management
  • Data processing and analysis
  • Data output and presentation: Maps/tables/figures/video/audio/3D models
  • Various interaction techniques: mouse, keyboard, Voice, 3D mouse, VR (view, voice, motion, tasting, smelling)

Capabilities of GIS

  • Data capture/input: …Input data by digitizing, scanning, or direct coordinate entry…
  • Edit data in the GIS to correct errors or add features
  • …Label the spatial features so they can be identified (names or codes)


  • Link attribute data to spatial objects
  • Link to external databases
  • Make changes in existing databases
  • Update database features
  • Import and export from/to other GIS or DBMS
  • Combine map sheets to create large databases
  • Match the edges of neighboring map sheets


  • …Make maps from different sources compatible so that they can be drawn on top of each other
  • Transformation of coordinates
  • …Projection change


  • Select features by their attributes: “find all districts with literacy rates < 60%”
  • Select features by geographic relationships: “find all family planning clinics within this district”
  • Combined attributes/geographic queries: “find all villages within 10km of a health facility that * have high child mortality”
  • Find all settlements that are more than 10km from a health clinic
  • Point-in-polygon operations: identify for all villages into which vegetation zone they fall
  • Polygon overlay: combine administrative records with health district data
  • Geocoding/address matching: match an address list with a street map
  • Network operations: find the shortest route from village to hospital


  • Identify or predict a process that has created or will create a certain spatial pattern
  • Diffusion: how is the epidemic spreading in the province?
  • Interaction: where do people migrate to?
  • …What-if scenarios: if the dam is built, how many people will be displaced?


  • Visualize pattern and identify anomalies
  • Compare information in map space and data space
  • Produce high quality map output for publication
  • Create a digital or paper census atlas
  • Export map output to other packages


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