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Spatial Models and Modeling. June 7, 2013 Institute of Space Technology, Karachi. Chapter 13: Spatial Models and Modeling. Model. Description of reality Static reproduction that represents basic shape and form of an object A conceptual description of key elements and processes in a system

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spatial models and modeling

Spatial Models and Modeling

June 7, 2013

Institute of Space Technology, Karachi

  • Description of reality
    • Static reproduction that represents basic shape and form of an object
    • A conceptual description of key elements and processes in a system
    • Sophisticated replica of objects, events, or processes
  • For this class
    • Restricted to computer-based models of spatial features
computer based spatial models
Computer Based Spatial Models
  • Combination of
    • GIS
    • Computer programming languages
    • Spatial and non-spatial analytical tools
two broad classes
Two Broad Classes
  • Spatio-temporal Models
    • Dynamic in both space and time
    • Example: analysis of oil after spill
  • Cartographic Models
    • Static models
    • Involve application of spatial operations
    • Example: buffer, interpolation, reclassification, overly
    • Combine data from multiple data layers
cartographic models
Cartographic Models
  • Represent spatial features at a fixed point or points of time
  • Most GIS models are cartographic models that are temporally static
  • Provides information through a combination of spatial data sets, functions and operations
    • Reclassification
    • Overlay
    • Interpolation
    • Terrain analysis
    • Buffering,
    • Map algebra, etc.
example suitability analysis
Example: Suitability Analysis
  • Suitable park sites based on the proximity to Roads and Lakesand the absence of Wetlands
flow chart
Flow Chart
  • A graphic representation of the spatial data, operations and their sequence of use in a cartographic model
  • Land use planning
  • Transportation route and corridor studies
  • Design and development of water distribution systems
  • Human disease spread
  • Site selection
  • Pollution response planning
  • Endangered species preservation
designing a cartographic model
Designing a Cartographic Model
  • Spatial functions and operations are mixed and matched in cartographic models
  • Variation in sequence of same operations will result in entirely different outputs
  • With a small set of data layers and tools, a huge number of models can be created
  • Usually produces a large number of ‘intermediate’ or temporary data layers that are not needed in final output or decision making
designing the best cartographic model
Designing the BEST Cartographic Model
  • Selection of appropriate spatial tools and specification of their sequence
conti designing a cartographic model
Conti.. Designing a Cartographic Model
  • Based on a set of criteria
  • These criteria are usually defined in qualitative terms
    • The slope must not be too steep
  • Interpretation /translation of criteria into selection and sequence of spatial operations
    • What is meant by “too steep”
  • Need to be converted to specific, quantitative measures
example home site selection
Example: Home Site Selection
  • Problem: Ranking sites by suitability for home construction
  • Criteria:
    • Slopes should not be too steep
    • Southern aspect is preferred to enhance solar warming
    • Soils suitable for on-site septic systems
    • Sites should be far enough from a main road to offer some privacy but not so far as to be isolated

First convert these criteria into more specific quantitative terms

  • Check availability and quality of data
    • Do the required data layers exist for the study area?
    • Are spatial accuracies, spatial resolution and attributes appropriate for analysis
    • What level of map generalization?
  • If required data is not available
    • Obtain or develop the required data OR
    • Modify the goals
  • Explicit ranking of the relative importance of different classes or types of criteria
ranking and weighting
Ranking and Weighting
  • Ranking: Assignment of relative values within the same layer
    • How we rank a sandy soil vs. a silty soil in a soil layer
  • ‘Weighting’ – assigning the relative values of different layers
    • How we weight the values in an elevation layer vs. the values in a land use layer
ranking within criteria
Ranking Within Criteria
  • Each Criterion in cartographic model is usually expressed by a data layer or ‘criterion layer’
  • Each criterion layer is a spatial representation of some constraint or selection condition
    • Select site outside floodplain: Floodplain sites = 0, Upland sites = 1
discrete vs continuous ranking
Discrete vs. Continuous Ranking
  • Discrete: when input data are interpreted such that criterion data layer is a map of discrete value
    • Soil = Good, Bad
    • Slope = steep or acceptable
  • Continuous: ranks vary along a scale
    • Soils: Rated from 1 to 100 for construction suitability
weighting among criteria
Weighting Among Criteria
  • Criteria combined in spatial analysis – in overlay or addition process
  • How to weigh one layer over another?
    • How important is slope relative to aspect?
    • Will an optimum aspect offset a moderately steep site?
  • The relative weightings given to each criterion will influence the result
  • Different weights are likely to result in different suitability rankings
  • Easy to define when importance of the various criteria expressed on a common scale – money
  • Reducing all criteria to a common scale removes differential weighting among criteria
spatio temporal models
Spatio-temporal Models
  • Includes time driven processes within the framework of model
  • Feature boundaries, point feature locations, and attribute variables may change within model run
  • Complicated models