Geocode Addresses Quickly and Easily

How does address geocoding work?

There are different types of geocoding, with varying degrees of accuracy. Before we look at the more precise method that BatchGeo uses, let’s consider a popular method employed by many other geocoding services.

Interpolation geocoding

True to the name, this type of geocoding interpolates where an address resides based on verified points, often intersections for gridded streets. Let’s say you wanted to convert 160 Main Street in your home town into geographic coordinates.

1. First the street is found by matching the street name, direction and street type against a block range in the street center line database. It would be disambiguated from other Main Streets by using the city name or postal code, if available.
2. Once the geocoder has determined the street, it will use the street number to find the closest block. For 160 Main Street, it likely is aware of locations at each end of the 100-200 block of Main Street.
3. Next comes the interpolation, which is the least accurate part of this geocoding process. There are 100 potential addresses on that block, but realistically only a dozen or less properties on a block. The geocoder will guess that 160 is a little more than halfway down the block.
4. Another guess the geocoder has to make is how far off from the street to make the building. After all the building is not likely to be in the middle of the block, which is the data available from the center line database. Usually this is a global value set when the geocoder is configured. Generally you would pick around 50 feet from the address block. There is no way to know for sure how far back the building or building entrance is located, but 50 feet is usually close.
5. Finally, the geocoder has to choose a side of the street to place the address. In many cities, odd and even numbers are consistently on opposite sides of the street. This is not always the case and requires, at minimum, intimate knowledge of the geographic area to produce an accurate result.

As you can see, interpolation has several stages where the geocoder has to make a guess. Educated guesses can give you results that are good enough in average cases, but you’ll have outliers that can be off by a lot. For this reason, for the best accuracy, you should consider more precise types of geocoding.

Parcel geocoding

By comparison, parcel geocoding is much simpler, but it requires much more granular data. Rather the interpolating a point from other nearby points, parcel geocoding requires knowing the boundaries of each parcel. In other words, it knows where each lot, or parcel, is located.

To determine the location of 160 Main Street using parcel geocoding, the geocoder would look up that specific address in the parcel database. It would still need to be disambiguated from other Main Streets, but it would not need to interpolate the location based on block-level data. Parcel geocoding uses parcel-level data.

The geographic coordinates returned from parcel geocoders is most often the center point of the parcel. While this leaves room for some inaccuracy in cases where a building is to one side of a large parcel, in practice this method of geocoding is much more precise than interpolation.