Geog 469 GIS Workshop

Geog 469GIS Workshop

Data Analysis - 1

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

• Data manipulation operations (Tomlinson functions)– data availability data readiness

• Data analysis operations (Tomlinson functions)– data ready to put into system information

INPUT OPERATIONS OUTPUT

GIS operation context

After Figure 13.6 (Longley et al p. 296)

World

Conception

Measurement & manipulation

Analysis

Interpretation,Validation,Exploration

Many kinds of analysis

feedback

Various steps in workflow

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

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

Examples of data manipulation

• Coordinate transformations

• Raster resampling

• 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 expressione.g. Median Age > 45

• Spatial queriesSelect * from layer where [condition]Condition: based on spatial relationshipe.g. hospital within King Countye.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 use of Python script to measure more complex

geometric properties

• 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, ….

union

dissolve

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 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

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

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

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

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

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 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

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, [email protected]

• Instructors

2. Workflow DiagramUsing ModelBuilder

Nature of Transformations

In previous diagrambuffer, 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?

Sequencing Transformations

Determining criteria (factors)

Refining criteriaGeneral criteria

Refined criteria (binary scheme)

Refined criteria (continuous scheme)

Slopes not too steep

Slopes < 30 degrees

Far enough from road to provide privacy, but not isolated

300 meter < X distance to road < 2000 meter

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 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 displayMap presentation vs. Data exploration

Map presentation(presentation mapping)

Data exploration(Geovisualization)

Interaction between map and user

Low High

Public or private realm

Public Private

Information sharing or knowledge construction

Info sharing Knowledge 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 models? • What are some of the challenges and

issues to consider in spatial modeling?• How is geovisualization different from map

presentation?