Preparing reference data
Reference data is one of the key elements in an address locator because the text addresses and locations that you eventually geocode are matched against the attribute values of the reference features. Errors in the reference data cause poor matching quality. For example, if the geometry of the reference features is incorrect, the addresses that are matched to them will also be spatially incorrect. If the name of a reference feature is misspelled, correctly spelled addresses may go unmatched. There are several potential errors to keep in mind regarding your reference data. They are described below.
Incomplete reference data
Reference data may need to be updated from time to time. For example, if a new housing tract is added to the city street network, these additional streets, with their associated ranges and other properties, need to be added.
Only the elements that exist in the reference data are stored in an address locator. If these features are not added, when the address locator is searched for a street that falls within this region, no match will be found.
Spatial reference and geometry errors
The reference data, such as a street or point address feature class, is usually produced based on a specific spatial reference. The coordinate system adopted in the feature class determines how the features are georeferenced. When an address locator is created, information of the spatial reference is stored in the address locator. Locations of addresses geocoded against the address locator will be georeferenced on the same spatial reference. It is important to make sure that the reference data contains a spatial reference.
To draw a feature on a map, the feature is required to contain a valid shape or geometry. If it happens that the shape of features in the reference data is null or empty, addresses geocoded to these features will not be drawn since they will also contain null shapes.
Incomplete address attributes
The success of geocoding relies on the address attributes in the reference data. If the address attributes are incomplete or contain errors, such as incorrect address ranges or missing street names and ZIP Codes, matching the address to those features may fail. For address locators created based on the street address styles, features containing empty street names or street names such as UNNAMED STREET or UNNAMED will not be included in the address locator since an address cannot be geocoded without a street name. Thus, it is essential to review and correct the address attribute errors in the reference data.
The spelling of an address element in the reference data may differ from the spelling used in the address data. The misspelling of one or more elements will contribute to the lowering of the match score. It is important that the spelling in the reference data attributes be accurate and complete. If an address element is spelled using more than one method, the use of an alternate name table is advised.