Geog 469 GIS Workshop. Data Analysis

Transcription

1 Geog 469 GIS Workshop Data Analysis

2 Outline 1. What kinds of need-to-know questions can be addressed using GIS data analysis? 2. What is a typology of GIS operations? 3. What kinds of operations are useful for data manipulation? 4. What kinds of operations are useful for data analysis 5. What is the difference between analysis and modeling? 6. How does workflow help organize operations?

3 1. What kinds of need-to-know questions can be addressed using GIS data analysis?

4 Need-to-know questions Location - Where is the phenomenon? - Where does it occur? Extent - How far does it extend already? - Where are its limits? Distribution - Is there regularity or randomness in its spatial distribution? - What is the nature of that regularity? Pattern - Why does it take a particular pattern (form or structure) that it has? - Why should the spatial distributional pattern exhibit regularity? Association - What else is there spatially associated with that phenomenon? - Do these things usually occur together in the same places? Change - When did it first emerge or become obvious? - How has it changed spatially (through time)? Diffusion - What factors have influenced its spread? - Why has it spread in this particular way? Based on Nyerges Analytical Map Use, Cartography and Geographic Information Systems

5 2. What is a typology of GIS operations?

6 Typology of GIS operations Analysis is the core of GIS that transforms data into information INPUT OPERATIONS OUTPUT General typology Data manipulation operations data available operation data ready Data analysis operations data ready operation information to knowledge?

7 Detailed GIS operation typology After Figure 13.6 (Longley, Goodchild, Maguire, Rhind 2005, Geographic Information Systems and Science, p. 296) Interpretation, Validation, Exploration Various steps in workflow Analysis Measurement & manipulation Problem Conception feedback World Many kinds of operations

8 Transformation Framework between object-field(s) and object-field(s) TO: Points Lines Polygons Fields FROM: Points Lines Points->Points Points->Lines Points- >Polygons Points->Fields Lines->Points Lines->Lines Lines->Polygons Lines->Fields Polygons Polygons- >Points Polygons- >Lines Polygons- >Polygons Polygons->Fields Fields Fields->Points Fields->Lines Fields->Polygons Fields->Fields -> means relationship between object-field(s) and object-field(s); a relationship is implemented through a GIS operation (function) From Nyerges and Jankowski (NJ) 2010 Table 6.1

9 Selected Spatial Relationships Six spatial relationships for transformations Connectedness (topologic) Adjacency (topologic) Containment (topologic) Proximity (geometric) Overlap (geometric) Pattern (geometric) In Table 6.1 transformation operations primitive --relationship operation--> primitive Replace --relationship--> with the six relationships above to arrive at those in NJ Table ; how do we implement them?

10 3. What kinds of operations are useful for data manipulation?

11 Data manipulation Data creation Digitizing Vectorization (ArcScan) Data editing Topology editing (in ArcGIS geodatabases create relationships) 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 (between spatial surfaces) Rubber-sheeting (least-squares computation)

12 Examples of data manipulation Coordinate transformations Raster resampling Translation

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

14 4. What kinds of operations are useful for data analysis?

15 Data analysis Queries Measure Transformations Descriptive summaries Optimization Modeling Following Longley et al 2005

16 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

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

18 Transformations (vector) Simple spatial analysis that change datasets, combining them or comparing them to obtain new datasets Buffer Spatial overlay point in polygon operations e.g. # parcels within zoning area? polygon in polygon overlay with the added complexity (union, intersect, identity) Other commonly used Clip, dissolve, erase,.

19 union dissolve

20 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

21 Descriptive spatial 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 an 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

22 5. What is the difference between analysis and modeling?

23 Data analysis treats structure models and process models. Spatial modeling generally treats only process models, i.e., models over time. It is a rough distinction, do not worry about being specific, as no one else really is

24 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 Desktop performs dynamic segmentation, other software such as TransCAD, ArcGIS Network Analyst work on networks Finding the gradient path based on grid data ArcGIS Spatial Analyst least cost path Location-allocation problems Location for a new retail store, e.g. Starbucks? See EC58.1.2

25 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

26 Spatial modeling 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, but emphasize temporal modeling 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 over time

27 6. How does workflow help organize operations?

28 Workflow Example Location Suitability Using ModelBuilder

29 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 Spatial structure influence is the basis of the transformations, wherein time component address externally

30 Geodesign modeling workflow Six steps of geodesign analysis answer questions in three passes: 1) Scope - Why? 2) Design - How? 3) Implement - What? Where? When? Goal: move data, knowledge, and values into action Steinitz, C. (2012) A Framework for Geodesign, Redlands, CA: Esri Press.

31 Transformations within Geodesign Workflow Processes The geospatial problem: where to site gray-water facility within Green (King) County ; best place for siting water recycling facility Start with geodesign six stages of modeling For each geodesign stage apply the collection of transformations needed. Details in Nyerges and Jankowski 2010 RUGIS Spatial Data Transformation Tables NJ

32 End