How does geocoding work?
The geocoding process begins with input data provided by the user. For geocoding within Symmetry’s products, the input data consist of a pair of addresses—an employee’s home and work addresses. These address pairs can be provided one at a time or en masse.
Symmetry’s process normalizes the addresses, a process that is often sometimes called address standardization. This process changes addresses to adhere to the United States Postal Service (USPS) standards. These standards state that a standardized address is one that, “is fully spelled out, abbreviated using the Postal Service standard abbreviations (shown in Publication 28 or as shown in the current Postal Service ZIP+4 file), and uses the proper format for the address file.” This process fixes spelling errors, capitalization errors, and corrects abbreviations so that the address is in a format that matches the one preferred by the USPS.
After addresses are normalized, Symmetry verifies the addresses in a process that compares the now standardized address against the official USPS database to see if there is a match. Symmetry also validates that the USPS delivers to that address as part of this process. While this address validation process is not necessary for the purpose of determining what taxes apply to the address, it can be helpful for the benefit of other business processes where employers would want a valid mailing address for employees.
With the addresses in a normalized or standardized format, Symmetry then geocodes the addresses to either the rooftop level, street level, neighborhood level, or community level.
| Geocoded to Rooftop Level | The record was geocoded down to the rooftop level, meaning the point is within the property boundaries, usually the center. |
|---|---|
| Geocoded to Interpolated Rooftop Level | The record was geocoded down to the rooftop level using interpolation (educated estimations using street coordinates). The point may be in or close to the property boundaries. |
| Geocoded to Street Level | The record was coded to the street level (ZIP+4 for U.S., full postal code for CAN). |
| Geocoded to the Neighborhood Level | The record was geocoded down to neighborhood level (ZIP+2 for U.S.). |
| Geocoded to Community Level | The record was coded to the community level (ZIP centroid for U.S., 3-digit postal code for CAN). |
Rooftop level geocoding is the most precise level of geocoding available followed by street level and finally neighborhood and community level. Street level provides an area of about 10-20 households and still provides very accurate tax results. Community level geocoding is only used for addresses that do not geocode to a rooftop, interpolated rooftop, street level, or neighborhood level.
Symmetry utilizes the Geographical Name Information System or GNIS for identifying locations. The GNIS was developed by the U.S. Geological Survey to record information about the official names of places, features, and areas of all 50 states, the District of Columbia, territories, and outlying areas of the U.S. The GNIS contains more than two million geographic names in the U.S. and provides search results with topographic map indexing, longitude and latitude, and feature information among more. These names reference points on the earth and the names and codes will never change, which makes them excellent for keeping track of locations in a software application.
Together with the geographical coordinates of the addresses (latitude and longitude) Symmetry indicates the level of geocoding with a code, and the tax results.
