GIS Models (with a side of ArcCatalog) James Frew ESM 263 Winter

Transcription

1 GIS Models (with a side of ArcCatalog) 1

2 ArcCatalog GIS data explorer (like Windows Explorer, but understands GIS data) e.g., shapefile is single item instead of mulpple files like Add Data in ArcMap graphical previews metadata ArcToolbox execupon environment (like ArcMap without a map...) Metadata editor 2

3 Why ArcCatalog? Only in ArcCatalog Browse/examine GIS data without having to add it to a map Copy/move GIS data without having to keep track of component files & folders (Maybe) more convenient in ArcCatalog Create/edit metadata Geoprocessing individual tools complete models 3

4 ArcCatalog vs ArcMap: gotcha! They don t play well together A change you make in one won t always be visible immediately in the other Crashes more likely when both are running Work-around: Only run one at a Pme Quit ArcCatalog before starpng ArcMap, and vice versa NB: ArcMap Catalog window is not ArcCatalog 4

5 What s a Model? an analysis paaern step-by-step implementable strategy 5

6 Developing a GIS Model 1. idenpfy goals phenomena scales parameters vs. variables 2. idenpfy elements data operapons 3. implement layers funcpons/tools 6

7 GIS Models for Decision Support AnalyPcal Reducible to computaponal workflow Repeatable Same condipons + same assumppons = same answer Transparent it is beaer for stakeholders to argue in principal about the merits of different factors and how their impacts should be measured, than to argue in pracpce about alternapve decisions.» Longley et al, Geographic InformaPon Systems and Science, 2nd ed. 7

8 MulP-Criteria Models output = f(mulpple inputs) spapal overlay composite feature layer mulpple rasters aaribute combinapon binary models logical expression feature/cell yes/no common applicapon: sipng analysis index models combinapon formula feature/cell index (rank) value common applicapon: suitability analysis 8

9 Vector-Based Binary Model Combine layers UNION Query all relevant aaributes pass logical test 9

10 Raster-Based Binary Model Query all relevant aaributes pass logical test no need to combine: cells already line up 10

11 MulP-Criteria Analysis (aka Index Modeling) 1. IdenPfy criteria: What will decision be based on? Geographic datasets 2. Standardize factors Interval or rapo scales 3. Establish relapve importance: How much does each factor maaer? Numeric weights 4. Combine constraints and weighted factors Decision score 11

12 MCA Step 1. IdenPfy Criteria What measurable geographic phenomena affect the decision? NB: Different objecpves different criteria Constraints combine: Boolean logic result: yes/no Factors combine: weighted sum result: numeric score Result: GIS layers 12

13 MCA Step 2. Standardize Factors All factors must be Same interval (or rapo) scale must be possible to add them together Same ordering value score (e.g. "more suitable") Example: linearized score score = ( (raw raw min ) (raw max raw min ) ) (std max std min ) + std min Result: Reclassified GIS layers 13

14 MCA Step 3. Assign Weights Simple case few factors stakeholder consensus overall weighpng "obvious" (yeah right...) Not-so-simple case many factors stakeholder conflict overall weighpng not obvious Manually assign weights that sum to 1 Use analypcal framework (e.g., AHP) Result: numeric weights 14

15 MCA Step 4. Combine score = (weight i factor i ) (constraint j ) Easily implemented with map algebra Result: score layer 15

16 MCA Weights: Saaty s AnalyPc Hierarchy Process (AHP) 16

17 MCA Weights: AHP CalculaPon Shortcut 1. Fill in missing reciprocal scores 2. Normalize score columns 3. Sum normalized score rows weight vector 4. (opponal) Normalize weight vector 17

18 Vector-Based Index Model 1. Standardize relevant aaributes 2. Combine layers UNION 3. Weighted sum of standardized aaributes 18

19 Raster-Based Index Model 1. Standardize cell values 2. MulPply by criterion weights 3. Sum weighted criteria 19

20 Figure/Quote Credits IntroducPon to Geographic InformaPon Systems, 4th ed. ISBN Geographic InformaPon Systems and Science, 2nd ed. ISBN Geographical InformaPon Systems: Principles, Techniques, Management and ApplicaPons, 2nd ed. ISBN