Composite Geocoding in Arc GIS Heather Wolfe

Composite Geocoding in Arc. GIS Heather Wolfe

Some Geocoding Basics Ø Geocoding matches input addresses and zip codes with geometry from reference shapfiles. Ø The tool used to accomplish this is called a locator. Ø Locators have various strengths and weaknesses and produce data matches of varying quality. Their results are QC’d differently.

The Classic Trade-Off. The classic trade-off in geocoding is accuracy vs. % matched. Generally, the higher the percentage that you match, the lower the accuracy that you have overall.

The Zone Restriction Ø A “zone restriction” in a locator allows for more accuracy in a locator by not permitting matches with an incorrect zip code. Ø This reduces errors related to two cities having the same street, but also rejects otherwise good addresses with an incorrect zip.

The One Address Locator uses “one address”, or one point per address, data. Ø Strength: Accuracy Ø Weakness: Reduced matching Ø You choose whether or not to have a zone restriction Ø

The Street Locator Ø The street locator can match input data to street ranges or street intersections. Ø Strength: Increased matching and compensation for data input error. Ø Weakness: Accuracy Ø You choose whether or not to have a zone restriction.

The Composite Locator Ø Actually not a locator Ø A device that permits use of multiple locators on the same data set Ø Locators listed in descending accuracy Ø Unmatched data is put into the next locator as input data.

Strengths & Weaknesses of the Composite Strengths Ø Speed Ø Able to handle large amounts of data Ø More results than from one locator alone Ø Weaknesses Ø Accuracy Ø Not able to use interactive match Ø Some good addresses may be rejected as unmatched Ø

More Accurate Use of Composite

Less Accurate Use of Composite

The Composite-Like Structure Ø Ø Ø Within 1 geographic area One Address with Zone One Address Without Zone US Streets without Zone Individually rematch, QC and then merge Ø Ø Ø Within Multiple Geographic areas One Address With Zone composite One Address Without Zone Composite US Streets Without Zone Composite Individually rematch, QC and then merge

Troubleshooting your Composite Have you mapped your input fields? Ø Do all of your reference data files have the same projection? Ø Does your input field contain house number, street direction, street name and street type in one field? Ø Have you mapped your reference fields correctly? Ø Have you mapped your input address fields? Ø