Geog 469 GIS Workshop

1. Geog 469GIS Workshop Data Analysis - 1

2. Outline 1. What is a typology of GIS operations? 2. How do we use workflow process diagrams? 3. What is geovisualization? 4. Discussions

3. 1. Typology of GIS operations • Analysis is the core of GIS that transforms data into information • Data manipulation operations (Tomlinson functions) • data availability  data readiness • Data analysis operations (Tomlinson functions) • data ready to put into system  information INPUT OPERATIONS OUTPUT

4. GIS operation context Interpretation, Validation, Exploration After Figure 13.6 (Longley et al p. 296) Analysis Various steps in workflow Measurement & manipulation feedback Conception World Many kinds of analysis

5. Needs for data manipulation • Incompatible cell sizes and boundaries confound multi-layer raster operations. These ambiguities are best resolved by resampling prior to layer combination Image source: Bolstad 2005

6. Data manipulation • Data creation • Digitizing • Vectorization (ArcScan) • Data editing • Topology editing (only in Arc/Info coverage and geodatabases) • Raster resampling (co-registering different raster images) • Data conversion • Export/import (be aware of data loss due to incompatibility) • Conversion among coordinate systems • Coordinate transformation • Registration (control points) • Transformations • Rubber-sheeting

7. Examples of data manipulation • Coordinate transformations • Raster resampling • Shift

8. Data analysis typology • Queries • Measure • Transformations • Descriptive summaries • Optimization • Modeling Following Longley et al 2005

9. Queries (extract) • Attribute queries Select * from table where [condition] Condition: logical expression e.g. Median Age > 45 • Spatial queries Select * from layer where [condition] Condition: based on spatial relationship e.g. hospital within King County e.g. hospital 10 kilometers or farther from highway

10. Measure • Measure distance, area and parameter of a single feature • ArcToolbox or calculate fields • Use meaningful measurement unit (by converting geographic to state plane) • Make use of Python script to measure more complex geometric properties • Measure slope and aspect of terrain • Work with DEM • ArcGIS Spatial Analyst

11. Transformations (vector) • Simple spatial analysis that change datasets, combining them or comparing them to obtain new datasets • Buffer • Spatial overlay • Mostly translated into point in polygon operations • e.g. # parcels within zoning area? • But there are an array of operations for polygon in polygon overlay with the added complexity (union, intersect, identity) • Other commonly used • Clip, dissolve, erase, ….

12. dissolve union

13. Transformations (raster) • Map algebra for raster • Local function (also known as reclassification) • Neighborhood function (focal function) • filtering • Spatial interpolation • Deterministic (specific function) : IDW • Stochastic (probability) : Kriging • Use Geostatistical Analyst for those

14. Descriptive summaries • Capture the essence of a dataset in one or two numbers • Mean and standard deviation of attributes • It may not be included in the process diagram, but useful in gaining a overview of data and determining the appropriate data classification method for thematic mapping • Descriptive summaries of spatial features • Mean center and dispersion • Measure spatial pattern of vector data • hot spot detection methods: nearest neighbor, K function… • Work with “point” data • ArcToolbox - Spatial Statistics Tools • CrimeStat (freeware) by National Institute of Justice

15. Optimization • Problem-solving by optimizing objectives • That is, minimize cost or maximize benefit given constraints • Find the least cost path • Finding the best path based on link-node representation where cost information is attached • ArcGIS for Desktop – dynamic segmentation, other software such as TransCAD, ArcGIS Network Analyst • Finding the gradient path based on grid data • ArcGIS Spatial Analyst – least cost path • Location-allocation problems • Location for a new retail store? • http://www.geog.ubc.ca/courses/klink/gis.notes/ncgia/u58.html#SEC58.1.2 • ArcGIS for Desktop – location-allocation

16. Spatial Modeling • Modeling enables us to explore multiple alternatives • Evaluate the outcomes of different policy alternatives (i.e. “what-if scenario”) • Often used for dynamic simulation, providing rich visualizations of alternative futures

17. Spatial modeling defined • Definition 1: A sequence of different operations; aka. cartographic modeling (by Tomlin) • What if you want to change parameters and see what happens to outcomes? Want to automate the whole process? • ArcGIS ModelBuilder: Run entire workflow with one click • Definition 2: Process model embeds operations so as to predict what would happen with given input parameters • Range from simple to complex • Soil erosion = f (a, b, c, d); housing price = f (a, b, c, d) • Hydrological modeling: sequence of logics or rules • Test what-if scenarios • Seek out models developed by experts • Perform literature review to identify published models

18. Example: evacuation plan • Identify high-risk area which is likely to be congested in the event of wildfire given a limited amount of time • Congestion = function (network configuration, population density, weather, other) • What would happen if we build the road with different design? • Use the outcome of simulation to design a road

19. Defining characteristics of modeling • Involves multiple stages • How something will change over time • Incorporate the previous knowledge • Approximation of reality • Some assumption on circumstance • Experiment with scenarios or input parameters • Can compare different outcomes from varying scenarios or parameters

20. Multi-criteria decision modeling • Many decisions require the evaluation of multi-criteria • Different stakeholders commonly hold different “values” about what is important • Values can be translated into criteria (factors) • How should that importance of criteria be measured? • How can various criteria measurements should be combined? • Example: problems of hazmat transport • Save money, save human life, save environment, save all three to what degree, to arrive at agreed alternative?

21. Conflict resolution in multi-criteria method • Don’t negotiate on the alternatives… • Negotiate criteria, which are basis for alternatives • For example.. what should be included as important criteria? and what weight should we provide to those criteria? • Perform sensitivity analysis on alternatives, criteria, and weights to arrive at mutually agreeable outcome • Software: ArcGIS, IDRISI from Clark Labs, CommonGIS - all have capabilities

22. How can you gain insight? • Help file • Search by commonly used operation names • ESRI Library (manual) • Software website • User Support, User Forum • Make the use of available scripts • Previous work • Draw upon literature reviews • Web of Science for academic works • GIS magazines for professional works • UW-gis-l list • To subscribe, uw-gis-l@u.washington.edu • Instructors

23. 2. Workflow DiagramUsing ModelBuilder

24. Nature of Transformations In previous diagram buffer, buffer and recode are based upon spatial data transformation operations … - buffer: line to polygon operation - buffer: line to polygon operation - recode: point to point operation What is the basis of these transformations?

25. Sequencing Transformations

26. Determining criteria (factors)

27. Refining criteria

28. Determining weights

29. Combining the criteria using overlay then recode to a ranking

30. 3. Geovisualization defined • Create and use visual representations to facilitate thinking, understanding, and knowledge construction about human and physical environments at geographic scales of measurement From MacEachren

31. Geovisualization purpose • Foster greater user interaction and participation in the use of GIS as decision support tool • User can undertake a balanced appraisal of a geographic phenomenon; decision-makers can appraise the consequences of different representations • Increasing role of users

32. Geovisualization and maps • Why do we use maps? • Can we utilize a more “interactive” environment within GIS? • Facilitate thinking, understanding, and knowledge construction • Roles that a display can play Map presentation vs. Data exploration

33. Roles of a displayMap presentation vs. Data exploration

34. What are advantages of geovisualization compared to map presentation? • Query • You can make a simple geographic inquiry • See how message is sensitive to input data elements • Transformation • Data can be manipulated such that objectives can be served better; it helps you overcome the limitation of traditional cartographic products (e.g. choropleth map) such as • Cartogram: areal size adjusted to magnitudes • Dasymetric map: spatial overlay • Immersion • Expand the capacity to experience the world through virtual environment (3D representation of the world) • Data-rich environment (Lidar), Computing power (animation) • Facilitate distributed decision-making process

35. 4. Discussion questions • Why do we build models? • What are some of the challenges and issues to consider in spatial modeling? • How is geovisualization different from map presentation?