week 3 & 4 notes

• Geographic Information System (GIS)

  A unique concept with three distinct features: discrete thematic data layers, geo-referenced data, and map algebra & data combination
• Three Unique Concepts of GIS

  • Discrete Thematic Data Layers
  • Geo-referenced Data
  • Map Algebra & Data Combination
• Discrete Thematic Data Layers

  • Environmental example: The single data layer "soil" could be broken down into soil texture, soil physico-chemical attributes, soil depth, mechanical fractions, and parent material
• Geospatial data


  Has both spatial and thematic components. Spatial component includes absolute localisation and topological relationship. Thematic component can be studied considering the thematic, locational, or both aspects.
• Geo-referenced Data


  Map data registered within a common locational reference system, allowing information on different layers to be compared and analyzed in combination
• Map Algebra & Data Combination

  Combining and transforming information from different layers, sometimes called "map algebra"
• Why use GIS?


  • It is a rigorous and objective analysis tool for assessing complex environmental problems, and provides an excellent media for communicating the results to stakeholders
  • A majority of environmental questions or problems require some form of spatial analysis
• Basic Questions Asked with a GIS


  • What is at..._____? (Location)
  • Where is it..._____? (Condition)
  • What has changed...? (Trend)
  • Which is the best way...? (Routing)
  • What is the pattern...? (Pattern)
  • What if...? (Modeling)
• Computational Functions of a GIS System

  • Data Acquisition & Verification
  • Data Compilation
  • Data Storage
  • Data Update & Manipulation
  • Data Management & Exchange
  • Data Retrieval & Presentation
  • Analysis & Combination
• GIS As a Set of Interrelated Subsystems

  • Spatial and Attribute Data Base
  • Cartographic Display System
  • Map Digitizing System
  • Database Management System
  • Geographic Analysis System
  • Image Processing System
  • Statistical Analysis System
  • Decision Support System
• Spatial Database


  Defines the geography (shape & position) of spatial features
• Attribute Database


  Defines the characteristics and qualities of spatial features
• Georelational model


  Features and corresponding attribute records are 'tagged' with a common feature identifier
• Cartographic Display System


  Provides a means to create cartographic "map compositions" of all or selected portions of geographic data sets
• Map Digitizing System


  • Digitizing tablet
  • Scanner & interpreting software
  • Field data interpolation
• CAD - Computer Aided Drafting


  Related technology allowing for the development of digital versions of spatial map or blueprint data
• COGO - Coordinate Geometry


  Related technology allowing for the transfer of digitally captured field survey data into a spatial representation
• Image Processing System Examples

  • Arc/Info GRID
  • IDRISI
  • ERDAS-Imagine
• Statistical Analysis System


  Allows for the special manipulation of spatial data for statistical characterization and hypothesis testing
• Decision Support System (DSS or SDSS)

  Provides an interface for decision making and may contain automated decision algorithms for specific multi-criteria decision making tasks
• Advantages of digital versus analogue data

  • Easy to update
  • Easy and quick transfer
  • Small storage space required
  • Easy to maintain
  • Easy automated analysis
• Map


  A set of points, lines and areas (polygons) that are defined both by their location in space with reference to a co-ordinate system and by their non-spatial attributes

  
• Data Structures


  • Raster based GIS
  • Vector based GIS
• Raster based GIS


  Represents spatial data as an array of grid cells (or pixels), with each cell containing a value representing the attribute

  
• Vector based GIS


  Represents spatial data as points, lines, and polygons defined by precise coordinate values, allowing for explicit representation of spatial entities and associated attributes
• Vector data


  Comprised of lines or arcs, defined by beginning and end points, which meet at nodes. Locations of nodes and topological structure are stored explicitly.
• Hybrid organisation system


  Links a relational database for attributes with a topological one for spatial data, using a unique identifier to connect the two
• Elements in a vector based GIS

  • DBMS (Data Base Management System) for attributes
  • System that manages topological data
• Entity-relation model


  Considers entities as relevant spatial objects, attributes as their characteristics, and relations as mechanisms to connect entities
• Relational databases


  Data is stored in tables where rows represent objects/entities and columns represent attributes/variables. Relationships between tables are possible through common identifiers.
• Object oriented databases


  Entities are defined as objects with both attributes and operations. Objects belong to classes that can have their own variables and belong to super-classes.
• Global Positioning System (GPS)


  A set of hardware and software that determines accurate locations on Earth using signals received from satellites. Can be used for georeferencing, positioning, navigation, and time/frequency control.

  
• Forms of GPS equipment

  • Small hand-held units
  • 'James Bond'-type wristwatch units
  • In-car navigation systems
  • Back-pack units
  • Aircraft and ship mounted systems
  • Belt-mounted units linked to wearable computers
  • Mobile telephone installed units
• GPS system hardware


  Antenna, receiver, and datalogger/data-collector
• GPS system software


  Preplanning, post-processing correction, display/editing, and converting/exporting data
• System software


  Software to coordinate signal collection and storage, file manipulation, and file transfer to and from a computer
• Primary functions of system software

  • Preplanning
  • Post-processing correction of raw satellite data
  • Display/editing of the data
  • Converting/exporting of the data
• Preplanning


  1. Determining satellite availability for a particular place and time

  2. Preparation of data dictionaries for a particular job

  
• Correction


  Use of a base station file to apply corrections to the raw data collected from the satellites
• Editing and display


  Averaging points, connecting points to form lines or areas, smoothing, measuring distance and area, and displaying the data to screen