Introduction to Geographic Information Systems
Spring 2013 (INF 385T-28437)
Dr. David Arctur
Lecturer, Research Fellow
University of Texas at Austin
Lectures 8 & 9
Feb 28, 2013
8 - Spatial Analysis
9 - Geocoding
Geocoding Outline (Tutorial Ch.7)
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Geocoding overview
Linear (street) geocoding
Problems and solutions
Street map sources
Polygon geocoding
Geocoding in ArcGIS
Useful Web sites
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Lecture 9
GEOCODING OVERVIEW
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Geocoding


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Process of creating geometric
representations for locations (e.g., points)
from descriptions of locations (e.g., street
addresses)
Uses a computer program that employs
code tables to standardize address
components called a geocoding engine
Two ways to geocode
 Batch geocoding—attempts to match all addresses
 Interactive rematching—sophisticated user interface
to match addresses
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Geocoding examples

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City’s economic development department maps
technology businesses by street addresses to see
technology-rich areas in a city
County health director maps personal care and
nursing homes and compares them to elderly
population by neighborhood
Business maps store locations and compares to
competitor locations
Emergency dispatch operators geocode an address
to determine who should respond to an emergency
call
Others?
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Geocoding files
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Tabular data (text or dbase)
 Street addresses
 ZIP codes
 Latitude and longitude
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Geocoding files

Geographic data
 Street centerlines
 ZIP code polygons
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Other geocoding files

Lines
 Railroads, rivers
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Polylines
 Parcels, census blocks, tracts, MCD/CCDs, places,
counties, etc.

Points
 Landmarks such as churches, schools, and other
cultural features represented as TIGER as points
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Lecture 9
LINEAR (STREET)
GEOCODING
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Linear geocoding (streets)

Urban street maps
 Four street address numbers ranging from low to high for each
side of a street segment
100
101
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Oak Street
198
199
10
Geocoding steps
Original address: 125 East Oak Street 15213
Address parsed: |125|East|Oak|Street| 15213
Abbreviations standardized: |125|E|Oak|St|15213
Elements assigned to match keys:
[HN]:125 [SN]:Oak[ST]:St [SD]:E [ZP]:15213
Index values calculated:
[HN]:125 [SN]:Oak(Soundex # ) [ST]:St [SD]:E [ZP]:15213 (Index #)
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Geocoding steps
Candidates identified: 125 East Oak Street15213
From
To
Street
Type
Side
Parity
Direction
Street_
2
98
Oak
St
R
E
W
4344
1
99
Oak
St
L
O
W
4345
100
198
Oak
St
R
E
E
4346
101
199
Oak
St
L
O
E
4357
Candidates scored and filtered:
From
To
Street
Type
Side
Parity
Direction
Street_
100
198
Oak
St
R
E
E
4346
101
199
Oak
St
L
O
E
4357
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Geocoding steps
Best candidate matched
From
To
Street
Type
Side
Parity
Direction
Street_
101
199
Oak
St
L
O
E
4357
Oak St
98
100
198
1
99
101
199
Pine Av
2
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Address components
Number
123 Oak St E, Apt. 2, Pittsburgh, PA 15213
Street name
123 Oak St E, Apt. 2, Pittsburgh, PA 15213
Street type
123 Oak St E, Apt. 2, Pittsburgh, PA 15213
Direction, suffix
123 Oak St E, Apt. 2, Pittsburgh, PA 15213
Direction, prefix
123 E Oak St, Apt. 2, Pittsburgh, PA 15213
Unit number
123 Oak St E, Apt. 2, Pittsburgh, PA 15213
Zone, city
123 Oak St E, Apt. 2, Pittsburgh, PA 15213
Zone, ZIP code
123 Oak St E, Apt. 2, Pittsburgh, PA 15213
Items for single number street address:
Address
123 Oak St E
Unit
City
ZIP Code
Apt. 2 Pittsburgh 15213
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Lecture 9
PROBLEMS AND SOLUTIONS
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Possible problems
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Variations in street names
 Fifth Avenue, Fifth Ave., 5th AV
 Saw Mill Run Blvd, Route 51
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Data entry errors
 Fidth Avenue
 Sawmill Run
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Place Names
 White House, Heinz Field, Empire State Building
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Intersections
 Fifth Avenue and Craig Street
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Possible problems
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Zones
 100 Main ST 15101, 100 Main ST 16202
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P.O. boxes
 P.O. Box 125
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Missing street (TIGER) information
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Solutions
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Clean data before geocoding
Use postal address standards
 Publication 28 of the U.S. Post Office (2000)

Ultimate source on mailing address formats and codes
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Provides standard street address formats
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Standards include house number, prefix directional,
street name, street suffix, common unit designator
abbreviation for apartment, city, state abbreviation, fivedigit ZIP code, ZIP+4 extension
Use Standard Intersection Connectors
 &|@
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Solutions
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Use alias tables
Alias
Address
White House
1600 Pennsylvania Avenue
Heinz Field
100 Art Rooney Avenue
Empire State Building
350 5th Ave
 Points of Interest (POI) databases; gazetteers
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Assign house numbers in rural areas
Purchase or build high quality maps (field
verification)
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Lecture 9
STREET MAP SOURCES
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Caution: source has changed
TIGER/Line files

2000 Census street centerlines
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Caution: source has changed
TIGER/Line files
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Commercial sources for maps
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GDT / ETAK / TeleAtlas  TomTom.com
 All the big pioneers of streetmaps are now TomTom
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Esri StreetMap Premium for ArcGIS
 No more free streetmaps
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MapBox.com (free & fee)
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Others…?
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OpenStreetMap.org (free open-source)
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Lecture 9
POLYGON GEOCODING
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Polygon geocoding
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Suppose you wished to make a
choropleth map showing distribution of
attendees at an event
Need to geocode data whose identifier is
a polygon (e.g. ZIP code, city, or county)
 Create an aggregate table with a single record for
each unique polygon
 Count the records for each polygon
 Join table to corresponding polygon layer
 Symbolize with a choropleth map or graduated point
symbols
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Polygon geocoding (ZIP codes)
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Polygon geocoding (ZIP codes)
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Points created at ZIP code centroids
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Polygon geocoding (ZIP codes)
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Spatially join points to polygons to make
choropleth map
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Choropleth map result
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Lecture 9
GEOCODING IN ARCGIS
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Create address locator
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ArcCatalog
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Choose address locator style
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Skeleton of the address locator
Based on data tables and reference layer
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Choose reference layer
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Streets, ZIP codes
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Address locator properties
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Geocode in ArcMap
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Add tabular data and streets layer
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Add address locator
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Geocode addresses
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View geocoding results
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Interactively rematch addresses
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Address rematching
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Investigate unmatched addresses
 Generally requires expertise with knowledge of
local streets
 Compare street name in the attributes of streets
table and address table
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Prepare log file
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Log file includes reasons why addresses did
not geocode
Useful for future work on cleaning addresses
or repairing street maps
Incorrect address
Possible reason/solution
490 Penn Avenue
Missing ZIP code
111 Hawksworth
Spelled incorrectly
900 Smallman Street
TIGER street missing
900 Lib Ave
Spelled incorrectly
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Lecture 9
USEFUL WEBSITES
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Useful Web sites
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http://www.usps.gov/
http://www.geocode.com/ (TomTom fee service)
http://batchgeo.com/
http://www.mapquest.com
http://maps.google.com
http://www.bing.com/maps/
http://www.zipinfo.com
http://zipskinny.com/
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Others?
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Geocoding Summary






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Geocoding overview
Linear (street) geocoding
Problems and solutions
Street map sources
Polygon geocoding
Geocoding in ArcView
Useful Web sites
Complete Assignment 7-1 (7-2 optional)
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