Week 11 & 13 notes

• When we talk of data analysis it is paramount that we simultaneously deal with real world example of application potentials that often confront us
• The students shall only then get a proper orientation of the subject he / she is trying to learn
• Discussion of the precept alone may not at all be lucid to the students and just might scare them away from garnering further insight
• Geographic Information System (GIS)

  An automated information system that is able to compile, store, retrieve, analyze, and display mapped data

  
• Only a decade ago this technology was limited to a relatively small number of colleges, universities, and local, state, and Govt. agencies
• Types of GIS users

  • Systems users (who have hands-on use of the technology)
  • End users (who are users of the information generated by a GIS)
• GIS applications


  • Environmental research and model building
  • Urban demographic studies
  • Transportation analysis
• Its most important applications include those that support decision making
• Map data used by GIS

  Collected from existing maps, aerial photos, satellites, and other sources

  
• Converting map data to digital form

  Using a digitizer or similar device to make it computer compatible

  
• This transformation allows the storage, retrieval, and analysis of the mapped data to be performed by the computer
• Maps produced by a GIS are typically displayed on computer monitors or are printed on paper

  
• Unlike many other forms of computer graphics, such as computer-aided drafting/design (CAD) systems, a GIS displays actual geographic or mapped objects

  
• GIS is much more than a mapping system. What sets it apart from even the most sophisticated mapping system is its power to analyze data and to present the results of that analysis as useful information to assist decision makers

  
• For a GIS to accurately represent occurrences on the earth's surface, data must be reliable, accurate, and pertinent
• The success of the GIS and all decisions that are based on it ultimately rest on the integrity of the data
• The GIS must be capable of compiling, updating, and maintaining its data
• No matter how sophisticated the analytical tools, misused or questionable data will make the final output doubtful
• The adage "garbage in – garbage (often the output sold as Gospel by over-enthusiasts) out (GIGA)" certainly holds true in the world of GIS
• Use of GIS


  Driven by the need to answer geographical or spatial questions
• Logical flow chart of analytical operations within a GIS framework

  1. Initial geographic question

  2. Data collection

  3. Data conversion to digital format

  4. Data entry into database

  5. Data analysis

  6. Tabular output

  7. Cartographic output

  
• GIS database


  Contains both map data (depicting location of geographical objects) and attribute data (describing physical characteristics of each object)

  
• During a GIS analysis, site (map) data is linked with situation (attribute) data for each mapped object

  
• Map layers


  Individual spatial phenomena or map themes in GIS terminology

  
• Each layer comprises all of the pertinent map and attribute data

  
• The layered map model will be used throughout this discussion to give examples of GIS analysis and use

  
• Spatial questions that drive a GIS

  • What exists at a particular location on the face of the earth (locational analysis)
  • When is a specific spatial condition satisfied
  • What has spatially changed over time
  • What kind of pattern will emerge from geographical data
  • What will happen if certain phenomena are entered into predetermined scenarios
• Locational analysis


  Mapped data primarily indicates where objects are located, but cannot explain why
• GIS analysis may show a connection between paddy growth, soil type, and available water by simultaneously examining computerized crop, soil, and soil moisture maps

  
• Spatial analysts continually seek patterns in mapped data

  
• Satisfying a spatial condition


  Discovering whether the mapped data will meet certain conditions
• Temporal analysis


  Comparing maps of various dates to understand how the world is constantly changing
• Emerging patterns


  Seeking to know if two or more things vary similarly in space
• Evaluating different scenarios


  Employing models to forecast and map the potential impact of changes to assumptions
• Sensitivity analysis


  Testing different scenarios that vary assumptions and evaluating the response to determine how sensitive the model is to changes in assumptions
• Basic database requirements for a GIS

  • Incorporate (import) data from outside sources
  • Easily update and alter data
  • Ask data-related questions of (or query) the database

  
• Importing and expanding the database

  Data can be imported in standard ASCII files or manually entered
• The DBMS allows for error checking as new records are created or existing ones are updated
• A GIS must also provide the ability to create data files that can be exported to other systems
• Updating attributes


  Maintaining the currency of the data depends on updating capability