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Suitability Analysis in Raster GIS. Combining Multiple Maps. The Challenge. Thus far Single or Dual Factor Overlay Analyses i.e. Land Cover on Private Land Biophysical Analyses with Algebraic Formulas i.e. RUSLE Landscape Planning Dozens to hundreds of spatial factors
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Suitability Analysis in Raster GIS Combining Multiple Maps
The Challenge • Thus far • Single or Dual Factor Overlay Analyses • i.e. Land Cover on Private Land • Biophysical Analyses with Algebraic Formulas • i.e. RUSLE • Landscape Planning • Dozens to hundreds of spatial factors • Factors have “apples and oranges” characteristics • Combinations must reflect social values, not just (bio)physical processes • “Best” for industrial development – from whose perspective? • Therefore • “Suitability Analysis” is not objective - must typically be vetted by experts • If experts are not GIS experts (i.e. local stakeholders), suitability factors and their combination must be visually explained • “Weighting and rating” is a key opportunity for public deliberation
Suitability Analysis • General purpose • To rank potential sites according to suitability for a proposed type of activity • Requirements • A set of “factor” or criteria maps, organized to rate sites relative to one or more characteristics • A technique for appropriately combining factors
Types of Criteria • Absolute • Frequently hard-edged • Often include property ownership/management zones • Often involve legal standards • Relative • Typically “fuzzy” edged • E.g. “proximity to X” where closer = better, but no absolute distance known in advance • Often involved in trade-offs where values ranges come from specific data within a place • Criterion 1 = “Low rent” and criterion 2 = “close to school”
Suitable For Whom? • Suitability models have a “point of view” • Audience can be human • “Affordable housing” • Best sites for High-end commercial • Audience can be environmental • Best habitat for black bear • Most suitable multispecies conservation areas • Can be implicit or explicit • But better to be explicit where possible
Common Units • How do you “combine” • a map representing “meters to nearest road” • Units = meters • with another representing “land cost”? • Units = dollars • Short Answer: find or create common units • Easiest: likert scale “preference” units • A range of values: 1 to 5, or 1 to 9 • Polar opposites on both sides of range • i.e. “Best”/”Worst”, “Most Suitable”/”Completely Unsuitable”
Cautions with Likert Scales • Consistent Application • With multiple factors, must make sure that scale consistently applied • example analysis: want to be near streams and far from roads, using 1..9 with 9 = best • Calculate distance to streams, distance to roads • Reclassify stream distance to preference units • Closest = 0 distance = 9 • Reclassify road distance to preference units • Closest = 0 distance = 1 • In other words, may need to “flip” values when reclassifying • Doesn’t really avoid scaling issues, just defers • Sensitivity and range in price/distance may be different • Often what’s needed from initial analysis is “range of the possible”
Overview • Why Use ModelBuilder? • ModelBuilder Basics • Common ModelBuilder Problems • Advanced ModelBuilder
Why Use ModelBuilder? • An automation tool… • But comes with some startup overhead • Most useful in two circumstances • Documents models & their parameterization • Allows experimentation with model parameters – particularly for “weighting and rating” • Common Types of Models • ETL – Extract, transform and convert raw data • Suitability – Building attractiveness maps
ModelBuilder Basics • Basic idea is that of a “dependency diagram” • User specifies inputs, processing and outputs • If inputs change, system repeats intermediate operations as needed • Diagram has three kinds of elements • Inputs • Geoprocessing Operations • Outputs • Output from one operation can be used as input to an other, allowing “chaining”
ModelBuilder Setup • Rather obscure to start…implemented as a custom toolbox tool • Open toolbox panel • Create empty toolbox • Right mouse on Toolboxes, select New Toolbox • Create empty model • Right mouse on new Toolbox, select New Model • Then populate model by drag and drop • Of data layers from map table of contents • Of geoprocessing operations from the toolbox • Finally, wire data and processing boxes together
Example: Simple MB Model • Goal • Create a factor map expressing simple proximity to residential landuse where output is classed from 1..9 • Method • Create new model • Select residential landuse from San Miguel Parcels database • Add Euclidean distance geoprocessing operation • Connect landuse (input) to distance (process), specifying new grid (output) • Run • Add Reclass Operator • Connect output grid of distance operator to input of reclass, specifying new output grid • Run again
Review of Simple Model • Benefits • Multiple logical steps encapsulated in a single step • Model Logic Recorded in Diagram • Model Parameters Recorded • Problems / Caveats • Default is not to show results… • Model as Created is 100% specific to particular data paths/locations on disk • Model Saving Bizarre.. • Default operation names make no sense to end users • Spatial Analyst Toolbar Options do *not* inherit
Showing Results • Simple, but not Obvious • Right Mouse on Output -> Add to Display • If at first you don’t succeed, try toggling again
Saving / Finding Models • By default, models saved in “My Toolboxes” folder • Main menu Tools->Options->My Toolboxes • Default is C:\Documents and Settings\(Username) \Application Data\ESRI\ArcToolbox\My Toolboxes • Easiest to find in ArcCatalog/My Toolboxes • Can “Add Toolbox” stored on disk
Making Models Generalizable • Running Models • Can Double Click on Models in Toolbox Panel • By default, not too useful, because no user control of outputs • Generalizing Models • By default, models only use exact data originally specified • To make a model into a true “tool” need to specify which inputs / outputs are variable parameters • Right mouse on input or output • Select “Parameter” (toggle) • After Parameters are set, double clicking brings up user dialog
Making MB Diagrams Legible • All elements can be “renamed” from right mouse menu • Rename layers if necessary to clarify • Explain intent of geoprocessing operations • i.e. Isolate Residential Landuse instead of reclass1 • If Desired, change diagram properties • Square – Circle – Square • Box Background Colors • If you need better quality, export diagram…
Environment Variables in MB • Note • Spatial Analyst “Options” settings not inherited • Must explicitly specify for MB • Two options • Can do once for all toolboxes (recommended) • RM Top Toolbox->Environment Settings • General Settings -> Extent • Raster Analysis Settings -> Cell Size • Can do once for each model
Model 2: Weighted Overlay • Goal: • To Create an Attractiveness Model with ability to “Weight” factors • Method: • Create separate ModelBuilder models for each factor • Nest models into master MB model • Combine with weighted overlay
Model 2 Implementation • Factor 1: Proximity to Residential • Factor 2: Proximity to Ski Slopes • Created by copying and pasting factor 1 model and adjusting inputs and outputs • Weighting • Factor 1 = 2X Factor 2 • Use Spatial Analyst Weighted Overlay tool