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Using GeoDA. Software for Geo graphic D ata A nalysis and Exploration Developed by Luc Anselin Arizona State University School of Geography and Planning geodatacenter.asu.edu. Software for Spatial Analysis and Statistics. ArcGIS 9 The most common GIS Software, but $$$$!

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using geoda

Using GeoDA

Software for Geographic Data Analysis

and Exploration

Developed by Luc Anselin

Arizona State University

School of Geography and Planning

geodatacenter.asu.edu

Briggs Henan University 2010

software for spatial analysis and statistics
Software for Spatial Analysis and Statistics
  • ArcGIS 9 The most common GIS Software, but $$$$!
    • Spatial Statistics Tools for point and polygon analysis
    • Spatial Analyst tools for density kernel
    • GeoStatistical Analyst Tools for interpolation of continuous surface data
  • OpenGeoDA, Geographic Data Analysis by Luc Anselin now at Arizona State
    • Download from: http://geodacenter.asu.edu/
    • Runs on Vista and Windows 7 (also MAC and UNIX)
    • Earlier version called GeoDA runs only on XP (0.9.5i_6)
    • Easy to use and has good graphic capabilities
  • CrimeStat III download from http://www.icpsr.umich.edu/NACJD/crimestat.html
    • Standalone package, free for government and education use
    • Calculates values for spatial statistics but no GIS graphics
    • Good documentation and explanation of measures and concepts
  • R Open Source statistical package,
    • originally on UNIX but now has MS Windows version
    • Has the most extensive set of spatial statistical analyses
    • Difficult to use
    • Need to learn it if you are going to do major work in this area
  • S-Plus the only commercial statistical package with good support for spatial statistics
    • www.insightful.com

Briggs Henan University 2010

geoda overview
GeoDA Overview
  • GeoDA is a package for exploratory analysis of geographic data.
  • Primarily analyzes polygon data, but can also do some things with point data
  • Has major capabilities not easily available elsewhere including:
  • --creates spatial weights matrices with multiple options
  • --linking and brushing between maps, histograms, scatter plots
  • --calculates and maps Local Indices of Spatial Association (LISA or local Moran’s I).
  • standard multiple regression full diagnostics for spatial effects
  • spatial autoregressive model for both spatial lag and spatial error models
  • Free. ArcGIS not required, but it does require a shapefile for data input.

Briggs Henan University 2010

obtaining geoda software
Obtaining GeoDA Software
  • The GeoDA program is on my Web site at:

www.utdallas.edu/~briggs or go to

http://geodacenter.asu.edu/

You will have to create a new user account

  • download, unzip, and click the file OpenGeoDA.exe to start the software
    • This version (OpenGeoDA) runs on Vista and Windows 7
    • Earlier version (GeoDA095i) only runs on XP
  • it does have some “bugs” so some things may not work or it may crash!

Briggs Henan University 2010

help and documentation for geoda
Help and Documentation for GeoDA
  • For help using OpenGeoDA, go to

http://geodacenter.asu.edu/

Click on Support tab

  • For printable manuals, go to

www.utdallas.edu/~briggs and download geoDAdoc.zip

    • Geoda_quickstart : 25 page quick start guide to using geoda (read first)
    • Geoda_spautoa quick guide to spatial autocorreletion measures (read next)
    • Geoda93_manual is a 125 page manual which fully documents the software
    • Geoda 95i_updates is a 64 page manual which covers bug fixes and enhancements in the latest release
    • Note, all the above are written for the earlier version GeoDa9.3, not OpenGeoDa but differences are small

Briggs Henan University 2010

opengeoda interface 1 of 2
OpenGeoDa Interface: 1 of 2

Display and Create

  • File—open a shape file: it should also contain the data to analyze
  • Edit—copy maps, and open new maps to compare
  • Tools—create spatial weights matrices (very good)

create shapefiles: Thiessen polygons, centroids, etc

create shapefiles from .dbf containing X,Y coordinates

  • Table—Open a table (>Promotion), joins, variable manipulation, joins, etc.

To access more options, right click on any open window

Briggs Henan University 2010

opengeoda interface 2 of 2
OpenGeoDa Interface: 2 of 2

Analyze

  • Map—create many types of choropleth maps
  • Explore—creates various non-spatial graphs of data
  • Space—calculating Spatial Autocorrelation measures
  • Methods—standard and spatial simple and multiple regression
  • Options—lists options for the currently active window.

To access options, right click on an open window

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data for demo
Data for Demo

www.utdallas.edu/~briggs

china.zip

geoDAdata.zip

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1 use geoda to find the centroids of the provinces of china
1. Use GeoDA to find the Centroids of the Provinces of China

(Need ArcInfo to do this in ArcGIS, which is expensive. GeoDA is free. )

--Input the provinces shapefile: File>Open Shape File China.shp

--Open the data table: Table>Promotion to see what is there

--Create centroids for each province:

Options> Add Centroids to Table

Place check mark in X coordinates and Y coordinates box, click OK

--X and Y centroid coordinates are added to the table

--to keep them permanently you need to save as new shapefile

Table> Save to Shapefile asChina_Centroids.shp

--to close these files and start something new: File>Close All

Briggs Henan University 2010

2 create thiessen polygons for provinces of china
2. Create Thiessen Polygons forProvinces of China

--use point file of province centroids created

--Start the tool: Tools>Shape>Points to Polygons

Input File: China_Centroids.shp

Output file: China_Thiessen.shp

Bounding Box: leave blank (establishes outer edges)

--click Create, then Close

--Display the Thiessen polygons

File>Open Shapefile> China_Thiessen.shp

If a map window is already open, use:

Edit>New map layer> China_Thiessen.shp

Result not good because of outer boundary problem

--to close these files and start something new: File>Close All

Briggs Henan University 2010

3 explore data with different maps illiteracy for provinces of china
3. Explore data with different mapsIlliteracy for Provinces of China

-- Input the provinces shapefile, with data:

File>Open Shape File ChinaData.shp

Map window opens showing China provinces

--To see the data: Table>Promotion

(variables are defined in the file: chinaProvinceData.xls)

--To map the data, right click on the map window and select

Map >Quantile

Select variableto map: 1st variable: Illiteracy (% illiterate)

(note: default variable via Edit>Select variable does not work)

--Multiple different choropleth maps available:

Quantile, percentile, box map, std dev, equal interval, natural break

choropleth map: color polygons based on variable value

--Draw a second map:

Edit>Duplicate map (to use the same data set)

Edit>New map layer (to use a different data set)

different choropleth map types always examine different map types and number of classes

(Assumes a Normal distribution)

25%

25%

23%

23%

14%

34%

34%

14%

-2

-1

0

1

2

-.68

.68

0

Different Choropleth Map Types:Always examine different map types and number of classes!
  • quantile (note the frequency counts in the map legend!)
    • classes have equal numbers (quantities) of observations(equal areas under the frequency distribution)
    • If use 4 categories called quartile (quarter) map
    • Each has 25% of data
  • equal interval (note the frequency counts!)
    • classes are equal width on variable
    • will have different numbers of

observations

  • standard deviation
    • categories based on
    • 1,2, etc, SDs

above/below mean

    • Classes have different

numbers of observations

Equal area %s

Equal interval %s

Standard Deviation

Equal interval score

Equal area score

  • natural breaks
    • finds “natural groupings” by minimizing the
    • variance within each class using Jenks optimization.
  • Percentile
    • Similar to quantile with 4 cabut
  • Box map
different choropleth map types identifying the extremes box map
Different Choropleth Map Types:Identifying the extremes: Box Map

We are often interested in outliers: observations with very large or very small (extreme) values

Box map examines extreme data values

Possibly no observations in the extreme categories

Map<Box with “hinge” = 1.5 :

  • Similar to quantile map with 4 categories
  • adds “extreme” categories for data with values which are 1.5 (or 3) times the interquartile range

(difference between 25% and 75% percentiles)

  • Extremes here are based on the data value itself.
    • Maybe no observations in the extreme categories
    • always look at the frequency counts in the legend
different choropleth map types identifying the extremes percentile map
Different Choropleth Map Types:Identifying the extremes: Percentile Map

We are often interested in outliers: observations with very large or very small (extreme) values

Percentile map examines extreme percentages of data

Always have observations in the extreme categories

Map>Percentile with “hinge” = 1.5 (or 3):

  • Similar to quantile map with 4 categories except
  • Uses percentiles to identify extremes: top & bottom 1% & 10%.
    • Extremes are the tails of the distribution.
  • Extremes here are based on the data value itself.
    • Always* have observations in these categories, but they may not be extreme (*in theory, but sometimes not!)
4 box plots and frequency distributions
4. Box Plots and Frequency Distributions
  • Close all windows
  • Explore>Box Plot

repeat for illiteracy, urban pop %, NatGrow05

  • Explore>Histogram

repeat for illiteracy, urban pop %, NatGrow05

The Box Plot:

  • all observations are positioned based on their value on the variable
  • the green asterisk is the median observation
  • The blue line is the mean
  • the colored center section shows the 25-75% percentile
  • the red T line in the upper part shows the location of upper “hinge”
  • (value which is 1.5 times the interquartile range above the mean)
  • the red  in the lower part shows the location of lower “hinge”

(value which is 1.5 times the interquartile range below the mean)

  • --sometimes both Ts are at the top & bottom of box (as in crime data), so no observations are beyond the hinge
  • --sometimes no Ts show at all—if they are within the interquartile range

Briggs Henan University 2010

5 linking between maps and plots
5. Linking between maps and plots
  • Edit>Duplicate Map to create map layer
  • Right click, and select Map>Percentile

repeat for illiteracy, urban pop %, NatGrow05

(ignore warnings)

widen the legend box so that you can see frequency count

arrange boxes as illustrated

note that <1% has 0 observations for Urban pop, NatGrow

--the reason for warnings

Linking

  • click a province on the map :
    • it’s highlighted on other maps and plots!
    • click a data point in a plot, it shows on the map
      • If not, maybe it’s too small to see (e.g. Hong Kong): use zoom

Briggs Henan University 2010

warning about missing data
Warning about Missing Data
  • Often, value for some observations on some variables are missing
    • e.g. for Macau, or the Taiwan islands near the Fujian coast
  • Can cause big problems with results of analyses and with plots (such as the box plot)
    • Software often assumes value is zero
    • Big mistake
  • Observation should be:
    • Omitted
    • Insert average for the variable
    • Use an estimate (provided you have evidence)

Briggs Henan University 2010

6 moran s i and lisa

6. Moran’s I and Lisa

Briggs Henan University 2010

6 1 create spatial weights matrix
6.1 Create Spatial Weights Matrix
  • Create File: Go to Tools>weights>create

Input file: chinadata.shp

Queen contiguity

Click Add ID Variable(using existing variable does not work)

Enter new variable name: Poly_ID

Click Save to DBF Click—Yes, its safe

Click Create and name the file: ChinaData.gal

A new file ChinaData.gal is saved in the folder with

  • Check File: Go to Tools>Weights>Properties
    • Enter name of weights file
    • Histogram (frequency distribution) showing number of neighbors
    • Polygons with zero neighbors are potential problems (4 in this case)
    • Click on zero column and they are highlighted on map (Linking)
    • Open table (Table>Promote) and they are highlighted in table

Briggs Henan University 2010

format of gal file
Format of .gal File
  • .gal file is a .txt file:
    • open with Notepad

0 35 ChinaData POLY_ID

1 0

2 1

30

3 6

25 14 11 6 5 4

4 5

23 9 6 5 3

5 6

30 14 13 9 4 3

  • First line: 4 items: 0, Number of observations,
  • filename, IDvariable
  • All subsequent lines are in sets of two:
    • ID, number of neighbors
    • List of neighbor IDs
    • ID, number of neighbors
    • List of neighbor IDs

Hainan

Macau

Briggs Henan University 2010

6 2 calculate moran s i
6.2 Calculate Moran’s I

Calculate Moran’s I: Space>Univariate Moran

  • Variable: IlliteracyClick OK
  • Select Weight: ChinaData.gal Click OK
  • Moran Scatterplot opens
    • W_Illiteracy on vertical (Y) axis (neigbors)
    • Illiteracy on X axis
  • Moran’s I is .2047

Briggs Henan University 2010

6 3 statistical significance via simulation
6.3 Statistical Significance via Simulation

Check Statistical Significance via Simulation:

  • Right Click on scatterplot and select Options>Randomization

Select 999 permutations

Click Run for additional simulations and to check sensitivity of results

  • If p-value < .05 then statistically significant
  • Note numbers at bottom:
  • I: 0.2047: Morans I
  • E(I) -0.294: Expected value
  • for Moran’s I if random (no SA)
    • same for every simulation
  • Mean: of the sampling distribution
  • Sd: Standard Deviation of Sampling Distribution (Standard Error)
    • Change each simulation

I=.2047

Briggs Henan University 2010

6 4 calculate anselin s lisa local moran s i
6.4 Calculate Anselin’s LISA (Local Moran’s I)
  • Calculate LISA: Go to Space>Univariate LISA
  • Variable: IlliteracyClick OK
  • Weights: chinadata.gal Click OK
  • Place checks in top 2 boxes
  • We discussed these maps in

our last lecture

Briggs Henan University 2010

6 5 saving results of lisa analysis
6.5 Saving Results of LISA Analysis

Save spatial lag and standardized (z scores) for variable analyzed

  • Right-click Moran scatterplot and go to Save Results.
  • Check the boxes you want
  • Optionally, change the default

variable names

  • Save LISA scores, relationship type*, and probability level
  • Right-click significance or cluster map and go to Save Results.
  • Check the boxes you want
  • Optionally, change the default
  • variable names
  • *1: high-high, 2: low-low, 3: low-high, 4: high-low

To permanently add the new variables to the table, right-click on the table and go to SaveShape File As....

Briggs Henan University 2010

6 6 recomputing moran s i for selected observations
6.6 Recomputing Moran’s I for selected observations

The Moran's I slope and value can be recomputed for all observations excluding the ones selected:

  • Right-click on Moran scatterplot and choose Exclude Selected

Exclude selected observations

  • Click an individual observation or drag a box and Moran’s I is recomputed excluding selected observation(s)
    • New value shown in red on top right
    • Exclude observations also highlighted on maps

Exclude groups of observation by brushing

  • Hold Ctrl key and draw a rectangle; release mouse, then release Ctrl key; rectangle flashes;
  • Use mouse to move rectangle across screen
  • Moran’s I recalculated excluding observations within rectangle

Note: not a true Moran's I since lag-X not adjusted for excluded observations.

Briggs Henan University 2010

hints on getting your data into geoda
Hints on getting your data into geoda
  • Data (variables) must be in a shapefile, or in a .dbf which you join to the shapefile using Table>Join tables
  • a shapefile also stores data in a .dbf file which you can edit to add variables

How do I edit a .dbf file to add data?

  • Use Excel 2003 or earlier
    • You can save files from Excel in .dbf format
    • Excel 2007 or later will read but not write .dbf files
  • Use OpenOffice from Sun/Oracle

www.openoffice.org

An almost exact replica of Excel which is free

Briggs Henan University 2010

spatial data creation
Spatial data creation
  • geoDA also contains some capabilities for creating shapefiles: see Tools>shape

Briggs Henan University 2010

what have we learned today
What have we learned today?

How to use geoDA for

  • general exploration of spatial data
  • analysis of spatial autocorrelation

Next time

  • spatial regression
  • Then, using geoDA for spatial regression

Briggs Henan University 2010