Basic GIS Modeling - Suitability Index

1. The Delphi approach  
        a procedure for obtaining and processing expert judgments to
maximize the accuracy of the resulting estimates

Main considerations  
        data, budget, and time constraints for a scientific evaluation
        human mind is capable of making quite accurate judgments

The Delphi steps  
        1. ask each expert for an independent opinion on carefully
            prepared questions
        2. calculate the median and range of opinions and feed these
            back to the experts for another round of estimate
        3. repeat step 1 and 2 for a few rounds
        4. use the median of the final round as the best answer
        * time and cost factors

Experts' role
        1. select appropriate variables
        2. estimate magnitude of the ranking
        3. assign the weights

2. Land Suitability Analysis (LSA)
        Richmond Parkway, NY evaluation: McHarg, I.L., 1969. Design with
Nature. Doubleday/Natural History Press, New York.

        1. 16 land variables
                e.g. slope, drainage, bedrock foundation, land values  
        2. the variables are ranked by numeric numbers
        3. each variable is weighted from 1 to 3
                e.g. slope<2.5%,1; 2.5%<slope<10%,2; slope>10%,3
        4. the grand index = summation of ranking x weighting

3. The DRASTIC model
Development
        By the National Water Well Association in 1987 for US EPA to evaluate groundwater pollution potential.
        It used the Delphi method to design parameters by compiling responses from more than 40 of the nation's leading groundwater scientists.

The model
        D - Depth to water table
        R - Recharge
        A - Aquifer media   
        S - Soil media
        T - Topography
        I  - Impact of vadoes zone
        C - Conductivity of the aquifer

Limitations
        It provides a relative evaluation and is not for absolute answers. It is designed as a planning tool and should not be used for site-specific evaluations.

4. The Judgment Impact Matrix (JIM)
        It suits for evaluation of complex systems

Estimation structure
        components -> environmental elements -> societal elements
        -> grand index

The matrix
        components x link(0,1) x element set1 x element set2
                         x weights (for element 2)

The links, environmental, societal and weights are determined by Delphi
 
 
 
 
 
 
 

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