Geocoding Accuracy and Precision
What exactly is a rooftop geocode lookup? In order to answer that let's talk about what a geocode address is:
A geocode, or geocode address, is the latitude and longitude coordinates of a specified location on the planet (Earth). Let's take the Empire State Building: the address is 20 W 34th St, New York, NY 10118 and latitude 40.74861, and longitude -73.9852 is the geocode. It may seem intimidating but it's easy to find using a free geocoding tool.
The Empire State Building geocode above is an example of a geocode that lands at the street front. If we were to look at the White House (1600 Pennsylvania Avenue NW, Washington, DC 20500) and it's geocode latitude 38.897606, longitude -77.036674 the pin lands right on the roof of the building—which is called a rooftop geocode.
We've linked some neat tools here below, feel free to check them out!
|US Rooftop Geocoding||US Reverse Geocoding||Curious About Speed?|
In this article you'll walk away with enough knowledge to be dangerous on the following topics:
- Levels of Geocoding
- Why Rooftop Geocoding
- Risks of False Positives
- What Causes Errors in High-Quality Data
- Smarty Rooftop Geocoding
- Value: Needs VS Budget
Levels of 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 reality, there are several different accepted levels of geocoding. 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:
|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%|
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.
If you're trying to identify addresses within a block area, a Zip9 would be useful. If you're trying to identify addresses within a city or facility, Zip5 would be enough. For more information on these types of geocodes check out this article.
However, the most useful type of geocode is a rooftop geocode, placing that pin right on the roof of the building.
Why Rooftop Geocoding
We believe that rooftop means just that - on top of the roof of a building. And that's what you receive with Smarty's (formerly SmartyStreets) US Rooftop Geocoding.
Risks of False Positives
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 a big 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.
As mentioned above, many geocoding providers pass 'parcel-centroid' off as 'rooftop-level'. That can cause many issues, including general mistrust of your information, and lead to more manual work rather than eliminating it. You can see a full comparative breakdown in this article about the top address validation (and geocoding) tools.
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.
Looking for other red flags when vetting a geocoding provider? You can check out this webinar recording to learn 8 Questions to Ask When Selecting a Geocoding API.
Smarty 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!
What Causes Errors 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.
Smarty Rooftop Geocoding
Those who use Smarty for their geocoding needs get more bang for their buck. 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 as opposed to "rooftop-level" that's actually just parcel.
For international address geocoding, we include rooftop accuracy for many countries.
Value: Needs VS 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 or attribution requirements, or they prevent the storage of geocodes. Those "strings attached" might hurt your business model.
In contrast, Smarty provides a very generous Acceptable Use Policy.
Ready for hyper-accurate rooftop geocodes? Try our US Rooftop Geocoding demo and start getting geocodes in seconds.
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.