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Maximizing Accuracy

Objectives

• In this section you will learn a geocoding strategy that will produce the most accurate matches

Geocoding Strategy to Maximize Accuracy

This strategy is designed to be used in situations in which a high priority is placed on both the number of successful matches and the quality of those matches. Keeping in mind that there is generally a tradeoff between the number of matches and accuracy of matches, this strategy is designed to optimize the accuracy with the least possible impact to the match rate.

Overview

This strategy is based on using each of the relax options selectively on previously unmatched records, based on the reason(s) for the record not matching. This is because arbitrarily enabling a relax option for a record, regardless of the reason it did not match, can result in that record being matched incorrectly. Take for example, the following address:

Let's assume that the address was incorrectly input, resulting in the street type being incorrect. The correct address should have been:

A strict geocoding process returned a match code (lower case "t") indicating that the street type was not found.

Now, let's assume that, along with all other matched records, this address is re-attempted with the zip code relax option checked. The result is the following:

The use of the incorrect geocoding option resulted in address being matched to the same street name and house number, but located in the wrong zip code. In this case, relaxing the street type and not the zip code would have resulted in a correct match. Although this type of problem does necessarily occur often, it can be avoided through selective use of the relax options based on the match code returned on unmatched records.

Geocoding Procedure

Step 1 - Geocode all records with no relax options selected.

Step 2 - Select all unmatched records in which the directional prefix was not found.

Step 3 - Geocode selected records with the Directional Relax Option checked.

Step 4 - Select all unmatched records in which the Street Type was not found.

Step 5 - Geocode selected records with the Street Type Relax Option checked.

Step 6 - Select all unmatched records in which the Street Name was not matched.

Step 7 - Geocode selected records with the Street Name Relax Option checked.

Step 8 - Select all unmatched records in which the House Number was not matched.

Step 9 - Geocode selected records with the House Number Relax Option checked.

Step 10 - Select all unmatched records in which the Zip Code was not matched.

Step 11 - Geocode selected records with the Zip Code Relax Option checked.

Step 12 - After each individual option has been selected, you can optionally begin to search for combinations of match codes in order to identify records that did not match due to more than one reason (For example, neither a zip code and street type were not found for a particular address).

Selecting Specific Match Codes

The process of identifying records containing particular match codes can be accomplished with the following procedure:

Step 1 - Go to QUERY - SELECT BY VALUE

Step 2 - On the SELECT BY VALUE screen, select the option for By Expression and the option for Replace Selected, then press the button to the right of the Expression box in order to enter the Expression Builder (see below).

Step 3 - Once you are in the Expression Builder, use the example, below to create your query. The component of the match code that you are looking for should be enclosed in quotation marks (make sure to use the lower case version of the code since the upper case will only select records with successfully matched that component.

Next, use the dollar sign as the operator to indicated "contained within". The dollar sign should then be followed with the field containing the match code.

The sample expression below can be interpreted as:

Locate records in which a lower case "d" is contained somewhere within the MATCHCODE field.

Atlas Geocode Relax Options

The following table summarizes the Atlas relax options together with the associated match code and a query expression that can be used to select address records with the respective match codes.

*Assumes that the match code is contained in a field called MatchCode. If another field name is used, that name should be substituted in place of MatchCode.