Geocoding is the process of converting an address into a coordinate (coordinates are commonly referred to as “geocodes”). Many geocoding systems can also go a step further and determine the coordinates of place names like “The Grand Canyon,” where a set address may not exist. There are typically a few different levels of geocoding depending on your desired degree of precision:
ZIP+4 Geocoding (also sometimes called Street Level) will result in the geographic center of a 9-digit postal code (these codes originate as representations of one “delivery area” for the USPS) for any address within that code. The additional four digits usually narrow a postal code down to a specific block or street. You may have seen this complete 9-digit code when you enter your address somewhere like Amazon, and the site prompts you with “would you like to use this address instead?”. ZIP+4 geocoding is less precise than other methods but can quickly approximate an area that usually covers 10-20 separate buildings.
Interpolated Geocoding works by comparing an input address against known geocodes and interpolating the result based on a set of known address rules for the area (e.g., “each street has an odd side and an even side” or “Main Street has 50 addresses ranging from 100-150”). It is unique to an individual address, but the resulting coordinate may be anywhere on or near the actual physical property.
Rooftop Geocoding is the most precise method and utilizes granular structure data and other information to precisely pinpoint a property. The result is typically either the center of a structure or its entry point (like an entrance to a large office building or mall).
Uses of Geocoding
Because both addresses and coordinates have their own merits, you may want to employ geocoding to leverage the utility of each. You may do something like allow your users to enter their address but then store the coordinates of that address right alongside it behind the scenes. This would allow you to gain the benefits of coordinates while ensuring that your users only need to be concerned with their simple address.
You may have an address dataset but need coordinates for analysis and presentation. A geocoding service would allow you to gather coordinates for each address in your set quickly.
You may need to determine the exact distance between two buildings to assess the legality of a property line or new construction.
You may need to determine how many homes are within a certain distance to a public park. You could geocode all the addresses in the rough area of the park and then calculate distances to the geocoded boundaries of the park.
When we talk about physical locations globally, there are typically two ways of identifying them: addresses and coordinates. An address is a discrete identifier, usually for a building or specific plot of land. For example, you can go to 123 Main Street or 124 Main Street, but there’s probably no valid address between them. Valid addresses are typically maintained by the government in which they exist. A coordinate, however, is continuous and agnostic to political boundaries. Coordinates are represented by latitude and longitude values, where the latitude specifies the north-south position (-90° to 90°) and the longitude specifies the east-west position (-180° and 180°). When put together, these coordinates can select an exact location anywhere on the surface of the Earth regardless of whether or not that location is a valid postal address.
So why have two systems? Well, each has its benefits. Addresses are beneficial for organization and governance. They are an intuitive way of labeling a place with official semantic meaning (buildings, apartments, land parcels, etc.). They can certainly get complex, but they are created with an organizational scheme that follows prescribed rules (e.g., if you’re at 50 Main Street, you know the numbers will increase in one direction and decrease in the other). Addresses are readable, intuitive, and easy to converse about.
On the other hand, coordinates are relatively meaningless to the human eye; you probably can’t tell where “40.7484° N, 73.9857° W” is just by looking at it. There are several use-cases, though, where coordinates are pretty powerful. Coordinates cover every possible location globally rather than just the official addresses. The format and added precision mean you can quickly determine distances between locations or what timezone a location is in. Their lightweight nature means they are easily stored, analyzed by computer systems, or displayed to users on something like a map.