VIEWS: 11 PAGES: 35 POSTED ON: 3/30/2011
Geog 469 GIS Workshop Data Analysis - 1 April 20, 2010 Outline 1. What is a typology of GIS operations? 2. How do we use workflow process diagrams? 3. What is geovisualization? 4. Discussions 1. Typology of GIS operations • Analysis is the core of GIS that transforms data into information INPUT OPERATIONS OUTPUT • Data manipulation operations (Tomlinson functions) – data availability data readiness • Data analysis operations (Tomlinson functions) – data ready to put into system information GIS operation context Interpretation, After Figure 13.6 (Longley et al p. 296) Validation, Exploration Various steps in workflow Analysis Measurement & manipulation feedback Conception Real world Many kinds of analysis 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 Data manipulation • Data creation – Digitizing – Vectorization (ArcScan) • Data editing – Topology editing (only in Arc/Info coverage and geodatabases) – Raster resampling (coregistering 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 Examples of data manipulation • Coordinate • Raster resampling transformations • Shift Data analysis typology • Queries • Measure • Transformations • Descriptive summaries • Optimization • Modeling Following Longley et al 2005 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 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 the use of ArcScript to measure more complex geometric properties on the ESRI website • Measure slope and aspect of terrain – Work with DEM – ArcGIS Spatial Analyst 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, …. dissolve union 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 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, dispersion (use CrimeStat) • Measure spatial pattern of vector data – hot spot detection methods: nearest neighbor, K function… – Work with “point” data – ArcToolbox - Spatial Statistics Tools – Try CrimeStat by National Institute of Justice (freeware) 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 • Arc/Info workstation – dynamic segmentation, other software such as TransCAD, ArcView 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#S EC58.1.2 • Arc/Info workstation – location-allocation Need for spatial modeling • In reality, it is impossible to experiment on the real world • Instead, the model provides alternatives to experimenting on a digital replica of the world • Allows us to evaluate the outcomes of different policy alternatives (i.e. “what-if scenario”) • Can be used for dynamic simulation, providing decision makers with dramatic visualizations of alternative futures Spatial modeling defined • Definition 1: A sequence of different operations; aka. cartographic modeling (by Tomlin); process diagram – What if you want to change parameters and see what happens to outcomes? Want to automate the whole process? – Try Model Builder in ArcGIS: it allows you to run the whole procedures with one click • Definition 2: Process model (extracted from previous knowledge) is embedded in operations so as to predict what would happen 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 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 = f (network configuration, population density, weather, other) • What if we build the road with different design? What would happen? • Planners can use the outcome of this simulation to design the road 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 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? Conflict resolution in multi-criteria method • Don’t negotiate alternatives • Negotiate criteria, for example, what should be included as important criteria? and what weight should we provide to those criteria? • We can performance sensitivity analysis on alternatives, criteria, and weights to arrive a mtually agreeable outcome • Software: ArcInfo, IDRISI from Clark Labs, CommonGIS, GeoChoicePerspectives - all have capabilities How can you get help? • 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, email@example.com • Instructors 2. Workflow process diagram Using ModelBuilder 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? See…Nyerges and Jankowski 2010 RUGIS Spatial data transformation tables we look at these in more detail in next lec Sequencing Transformations Determining criteria (factors) Refining criteria General Refined criteria Refined criteria criteria (binary scheme) (continuous scheme) Slopes not Slopes < 30 too steep degrees Far enough 300 meter < X from road to distance to road provide < 2000 meter privacy, but not isolated Determining weights Combining the criteria using overlay then recode to a ranking 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 Geovisualization purpose • Foster greater user interaction and participation in the use of GIS as decision support tool • User can undertake a balanced appraisal of the message of a geographic phenomenon; decision-makers can appraise the consequences of different representations • Increasing role of users 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 Roles of a display Map presentation vs. Data exploration Map presentation Data exploration (presentation (Geovisualization) mapping) Interaction between Low High map and user Public or private Public Private realm Information sharing Info sharing Knowledge or knowledge construction construction 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 4. Discussion questions • Why do we build model given the fact that the model is an approximation of reality at best? • What would be challenges and issues to consider in spatial modeling? • How is geovisualization different from presentation mapping?
Pages to are hidden for
"Geog 463 GIS Workshop"Please download to view full document