CSISS - GIS Cookbook: Recipe - How to Geocode Addresses

GIS Cookbook: Recipe - How to Geocode Addresses

Keywords: Geocoding, geocoding services, geoprocessing, geodatabase, address matching, address number, locations, representations, reference theme, street, street name, zones, zip code
Category: Geocoding
Software: ArcGIS 8/9.x

Problem: I have a list of locations of armed robberies, how do I display these locations onto a map?

Description: Geocoding is the process of matching a particular address with a geographic location. This is done through matching records in two databases, one containing a list of addresses, the other containing information about a street network. The geocoding tool will match a given address with its unique position within the street network. Since the street network will already have been located in geographic space with reference to some coordinate system, assigning a given address on the street network also has the effect of locating that address in geographic space as well.

Scenario:
A criminologist wants to map the reported cases of armed robberies on businesses in Atlanta, Georgia, in order to reveal spatial patterns in the robbery data that may shed new light on the phenomenon. Such information can be used to predict future crimes or even as evidence against a known suspect. The criminologist is working with two files. One is a table of victimized business addresses and the other is an Atlanta, Georgia street shapefile.

Methodology:
The geocoding in this recipe will be done in ArcCatalog. Note that geocoding can also be done in ArcMap (Tools > Geocode Addresses).

1) Open ArcCatalog.

2) Find the address table you want to geocode.
See Pitfall 1

Note: The table icon should look similar to this.

Note: When opened, the table should contain an address field similar to the one in the example above.

3) Right-click on this table and select Geocode Addresses.

4) Select a geocoding service to use, then click OK.

Choosing a geocoding style.

-If no services are shown, then click Browse for service.

-If the desired geocoding services are still unavailable, they must be created. See "Creating a Geocoding Service/Address Locator".

5) In the Geocode Addresses window, the Address Input Fields should have been automatically set based on the geocoding service. If not, click on the dropdown list to choose the name of the column that has the correct address attribute.

6) Under Output shapefile or feature class click on the folder button to navigate to the folder in which you want to save your output file. Name this file, then click Save.

7) Click Advanced Geometry Options if you want to set the output coordinate system to something other than the coordinate system used by the reference (street) data.

8) Click Geocoding Options if you want to modify the settings used to match addresses to the street database. See "Creating a Geocoding Service/Address Locator" for more information on these settings.
See Pitfall 2

9) Click OK on the Geocode Addresses window to begin the address matching process.

10) After processing, a window will report the address matching results and provide an opportunity to re-process unmatched or poorly matched addresses.

11) Clicking the Match Interactively button opens a window that allows you to review the unmatched addresses one at a time. The unmatched addresses are shown in the upper half of the window. The selected address is highlighted in blue. The way the software parsed the selected address into individual address components is shown in the middle of the window and candidate street segment matches are shown at the bottom. If there is an obvious mistake in the way the address has been parsed, click the Modify button to fix the mistake. After fixing the mistake, an updated list of candidate street segments should appear. If one of these candidates is an acceptable match (note the Score value, with 100 being a perfect score), highlight the street segment and click Match.

12) Repeat the review process for each unmatched address, then click Close.

13) Click Done to finish the geocoding session.

14) To display your geocoded result, open ArcMap and add this file. Here is an example of the final product.

Note: The green points are the geocoded addresses.

Pitfalls:

1) Giving a street the wrong suffix or street type, like "Court" instead of "Avenue," or providing no suffix when there are multiple streets with the same name in the database, will cause errors. Misspelled street names or street names not in the database can also cause errors, although the software will try to match abbreviations and account for possible misspellings. This can be adjusted in the Geocoding Options window. It is also possible that there are errors or outdated information within the street database itself that could cause additional errors.
2) Street addresses are estimated along block faces; therefore, the true locations of the addresses may not be represented. For example, an address with a house number of 50 will be placed exactly halfway along the 0-100 block even though the actual location of the house is not likely to be at the exact midpoint of the street segment. Also, pay close attention to the offset setting (i.e., the distance from the street centerline the addresses will be placed). The offset can be adjusted in the Geocoding Options window.

Links:
Schlosser Geographic System, Inc. - Geocoding Issues, Alternatives, and Techniques
ESRI - Geocoding Extensions
GeoAccess - Geocoding Techniques

Authored by: Carlin Wong Modified: 4/4/05

Copyright © 2002-2015 by Regents of University of California, Santa Barbara Cookbook: Ben Sprague, Ethan Sundilson, Carlin Wong, Sam Ying

Copyright © 2002-2015 by Regents of University of California, Santa Barbara
Cookbook: Ben Sprague, Ethan Sundilson, Carlin Wong, Sam Ying