Geocoding Accuracy and Precision

Geocoding Accuracy & Precision Example

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Rooftop Geocoding

For geocoding US addresses, the geocodes that we return are based on our own data, as well as multiple private and public sources that interpret various data sets. We use all of these sources to give you true rooftop level accuracy.

For international address geocoding, we include rooftop accuracy for many countries.

Rooftop Accuracy Defined

We believe that rooftop means just that - on top of the roof of a building. And that’s what you receive with SmartyStreets’ US Rooftop Geocoding.

Finding the latitude and longitude for an address is a challenging task. The complexity is greatly compounded if absolute accuracy is required. As a result many other geocoding providers that advertise ‘rooftop level accuracy’ are actually providing you with ‘parcel-centroid’ geocodes. This means they are calculating the geocodes for the center of a parcel, and then calling it the “rooftop.”

In the cases of rural, large or irregular lots, the geocodes for the parcel centroid may actually be very far from the geocodes of the rooftop. And in multi-building lots, parcel centroid geocodes are inaccurate at best, and misleading at worst. This kind of inaccuracy can result in a large margin of error, sometimes as much as hundreds of feet. That’s big of a difference. Especially if you’re trying to determine if a property is in or out of a flood zone. If you are in the insurance industry, you know why flood zone proximity is important, and why you want true rooftop accuracy.

An easy way to see if a geocode provider is truly rooftop accurate, is to find and test their geocodes with farms, large apartment and commercial complexes, or irregular properties to see for yourself if the geocodes really hit the roof.

SmartyStreets technology provides true rooftop geocoding for the majority of addresses, not merely parcel centroid. This means we have some extra things running under the hood to identify the roof of the building no matter where it is found on the property. Because accuracy matters!

ZIP+4 Level Geocoding

Not everyone needs rooftop accuracy for their geocodes or wants to pay the price for that additional precision. Accordingly, we also offer ZIP+4 level geocoding based on public data that comes from the US Census Bureau and is known as TIGER data. The TIGER data we use for US addresses will interpret various data sets to give you block-level accuracy (rather than rooftop accuracy), and will be less expensive. Wikipedia has some excellent examples of how the interpreted results work.

For ZIP+4 level geocoding, we have about 38,683,796 unique lat/long coordinates for the US. Within that set, here is a breakdown of the various levels of geocode precision:

Precision Description Count Total
Zip9 9-digit ZIP precision. Usually block-level. 33,361,331 86%
Zip8 8-digit ZIP precision. 4,412,599 12%
Zip7 7-digit ZIP precision. 726,485 1.5%
Zip6 6-digit ZIP precision. 141,395 0.4%
Zip5 5-digit ZIP Code precision. Usually city- or facility-level. 41,986 0.1%

Why coordinates may be wrong, even in high-quality data

Even the highest-quality, curated data set may have errors. If a property has two structures on it, a modest house and a large barn that have similar rooflines, the barn may get tagged as the principal structure because of its size.

Further, assigning a precise latitude and longitude doesn't always automatically match up with a physical address. The mailbox for a house can be several hundred feet away from the actual house.

Weighing needs against budget

So which level of geocoding should you choose? That depends on the level of geocoding accuracy you need, and your budget.

If you can get by with block level accuracy most of the time, then our ZIP+4 level geocoder will probably suffice. If you need the highest accuracy geocodes available in the market, you’ll want to choose our US Rooftop Geocoding. If you aren’t sure, start testing your addresses. You will soon find out which level of accuracy you need.

One other thing to consider is what you plan to do with the geocodes that you receive. Most other geocoder providers offer geocodes with strings attached, like a restrictive Acceptable Use Policy, attribution requirements, or they prevent the storage of geocodes. Those ‘strings attached’ might hurt your business model.

In contrast, SmartyStreets provides a very generous Acceptable Use Policy.

Many users who use geocoding also use reverse geocoding. If you have latitude and longitude coordinates (geocodes) already and you want to learn how to convert them into addresses, you may want to get more information about reverse geocoding before committing to a particular provider.

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