Introduction to ArcGIS for Environmental Scientists Module 3 – GIS Analysis Address Geocoding

1. Introduction to ArcGIS forEnvironmental Scientists Module 3 – GIS AnalysisAddress Geocoding

2. Objectives • Learn what data and processes are required to convert street addresses to map coordinates

3. A table with street addresses to be mapped • An Address Locator to match addresses to reference data • Reference data, usually streets, that contains features to which the addresses are matched • Parcel-based reference data are thought to be more spatially accurate, but won’t necessarily result in more addresses being matched • Zip code-based geocoding will produce a high match rate, but locations will be placed in center of a zip code. Components

4. Address table Example The address locator parses the street address into number, name and type to find a match in the reference data Reference data attribute table

5. For each address, a list of potential matches (candidates) in the reference data is generated • Each candidate is scored between 10 and 100, where higher scores represent better matches • Candidate with the highest score wins, if it is above a minimum user-defined threshold • The output attribute table includes the match score and status: M = Matched, U = Unmatched or T = Tied • Rematch unmatched and tied addresses • Can be done in ArcMap or ArcCatalog Process

6. Data Quality • Unmatched addresses, or addresses matched with low scores, are usually caused by errors in the address table or reference data • Misspellings (“Carelton” vs. “Carleton”) • Missing information (e.g. street type) • Outdated reference data (missing newer streets)

7. Rematching Addresses • Used to match tied and unmatched addresses • There are three ways to rematch addresses: • Automatically by lowering sensitivity or minimum match score in geocoding options • Can result in matches in wrong locations • Manually by examining unmatched and low score matched addresses and correcting errors • Manually by selecting location on a map

8. Interactive Rematching

9. Using Online Geocoding Services • Address locator and reference data are located on the server • You add the locator in ArcMap and provide the address table • The service geocodes the addresses and creates an output feature class • You may set the geocoding options and all rematching capabilites are available, as if the process were run locally