What is a Geocode? What Is Geocoding?

Map with Geocode Example

A geocode is a set of latitude and longitude coordinates that correspond to a physical address or location. Geocodes can act as unique identifiers for entities and place names across the surface of the earth. For example, the rooftop geocode for The White House is 38.897606, -77.036674.

Geocoding is the process of finding the latitude and longitude coordinates that correspond to a location such as a physical address, city, subdivision, postal code. After completing the geocoding process, geocodes can be plotted on maps for navigation, spatial analysis, risk assessment along with other use cases.

Have addresses and need geocodes? Use US Rooftop Geocoding. Have geocodes and need addresses? Use US Reverse Geocoding. Batch geocode with US Bulk Address Validation.

In this article we'll cover:

Geocode Basics

A ‘geocode’ is just an easier way of saying ‘a latitude / longitude coordinate’—much in the same way that ‘geocaching’ is just an easier way of saying ‘coordinate based scavenger hunt.’ In other words, a geocode is the latitude and longitude coordinates for a specific location.

So, if geocodes are the lat long coordinates, then geocoding is the process of entering a location's description from one format (like a precise street address) and getting that location's specific lat long coordinates as the output. Geocoding can be performed in a number of different ways that differ in methods, costs, and results.

How accurate is geocoding?

Asking “How accurate is geocoding?” is like asking “How fast are cars?”. Neither question can be answered until we ask a more precise question. For example, if you asked a more precise question like, “How fast is a Ferrari F40’s 0–100 km/h?”. We can easily answer “4.1 Seconds”.

More precise question to ask about the accuracy of geocoding would be, “How accurate can geocoding be?” or “What accuracy of geocoding levels are available?” Those are questions worth answering. To give you the answers you need, let's discuss the four main types of geocode accuracy. They are, ZIP+4, interpolated, parcel centroid, & rooftop.

ZIP+4 Level Geocodes

ZIP+4 Centroid Geocoding Example

A ZIP+4 Code represents a postal delivery route within a larger ZIP Code that generally contains 10-20 addresses. The base of the ZIP+4 level geocode is simply the approximate center of that route. This makes these geocodes accurate to about the block level of the desired address and would look similar to the image here if plotted on a satellite image. This is useful when you only need the approximate location of an address without needing to know the precise rooftop or parcel.

Interpolated Geocodes

You may have heard of interpolation before, likely used by a math teacher. Interpolation isn't just useful in high school math classes, though. It's also used in other practices — like geocoding.

Interpolation adds speed to the geocoding process even though it is not the most accurate approach. Despite the complexity of the math involved, the concept itself is surprisingly simple, and it works like this:

Take a random street. For simplicity's sake, we'll say a residential street that terminates in intersections at both ends. Now let's suppose we have two geocodes that are in close-proximity to the addresses on the street we want to know about.

Let's assume those two reference geocodes are at either end of the street, that is, at either intersection. Once we have this information, we can use math to determine what's in the middle. When we use interpolation, we say, "Well, we start with point A, and we end with point D, so in between must be point B and point C."

Interpolated Geocoding Example

Fortunately, this method of determining geocodes is a process that can be automated by way of computer programs.

When we use math to determine where point B and point C are between point A and point D, the math puts the geocodes at regular intervals and set patterns, which is not necessarily the way that homes and businesses are built. The fact is, people put buildings wherever they feel like.

The precise rooftop geocode of a home may be far different from the interpolated geocode for that same home. The difference between the two geocode types becomes more pronounced in rural areas with larger lot sizes. When we use interpolation to create geocodes, we're creating geocodes that are "street-segment" accurate, but not "rooftop accurate."

Parcel Centroid Geocodes

Parcel centroid geocodes are calculated by taking the known boundaries of a property. Then, you approximate the geocode in the center of the parcel. Hence, the name “parcel centroid”.

Parcel centroid geocoding tends to be more expensive than ZIP+4 or interpolated due to the additional data needed to calculate the geocodes. Unfortunately, it still lacks considerable precision.

An important consideration with parcel centroid geocodes is that homes are often not built in the geographic center of the property. This is especially true in the cases of large or irregular parcels.

Parcel Centroid Geocoding Example

The purple markers on the image are parcel centroid geocodes provided by the Google Places Geocoding API. Notice how Google places the geocode in the pond?

A rule of thumb in geocoding is, the bigger a parcel, the less useful the parcel centroid geocode. Often, you need to pinpoint the roof of the home, and knowing the center of the parcel just isn't precise enough. Parcel centroid geocodes may fall hundreds of feet from the home or structure. Sometimes, they aren't even in the same postal code.

Rooftop Geocodes

Rooftop Geocoding Example

Having exact matches for a primary structure is on a parcel holds high value. In the case of insurance quotes, city planning, telecommunications and hundreds of other use cases, those dozens or hundreds of feet can be the difference between low and high liability. That is why rooftop geocoding exists.

Rooftop geocodes start with the parcel centroid geocode as the reference, which is then refined using additional data-points and calculations in order to match the geocode with the actual rooftop of the primary structure on the parcel. The more precise the geocode, the more expensive and difficult it is to obtain.

When looking for geocoder service providers, never trust that geocodes are truly “rooftop accurate” just because the provider says they are. Unscrupulous providers will often slap the “rooftop accurate geocodes” sticker on geocodes that are really only parcel centroid.

These providers count on you not checking the accuracy of their geocoder thoroughly before committing.

To ensure you are really getting the accuracy you need, test any geocoder you are considering with many parcels. Be sure to include large and irregular properties as well as suburban and rural plots in your testing.

Smarty (formerly SmartyStreets) provides true rooftop geocodes.

What Level of Geocoding Accuracy do you need?

ZIP+4 and interpolated geocodes are a lower price and lower precision. This makes them cost effective for some applications.

Rooftop-level geocodes are a higher price and far higher precision. This makes the cost effective for applications where hyper accuracy matters.

Parcel centroid geocodes are a higher price and lower precision. This makes the cost effective for few use cases.

In other words, parcel centroid geocodes are like a car that is also a boat. While it is a neat concept, an amphibious car is expensive and ends up being a poor quality car and a poor quality boat.

Who wants the worst of both worlds? For that reason, Smarty does not offer parcel centroid geocoding. We offer hyper-accurate United States Rooftop Geocoding. Where rooftop geocodes are not possible, we provide ZIP+4 geocodes.

What is geocoding used for?

Geocoding is used whenever someone needs to know the precise position of something on earth. We could write a book about what geocoding is used for but here are three examples to get you thinking.

  1. A restaurant franchise wants to send a coupon by mail to 300,000 addresses in a metropolitan area. The restaurant has ten nearby franchise locations and the company wants to print the address of the nearest location to each household.

    By geocoding all the addresses in the area, they can easily determine which restaurant address should be printed on each coupon. Less precise ZIP+4 geocodes would work here.

  2. An insurance underwriter needs to know exactly how far a home is from a nearby river. In this case, the home is on a 100 acre (40.469 ha) farm. A parcel centroid geocode indicates the home is 750 feet (0.23 km) from the river and would result in a low risk assessment and quote.

    A true rooftop geocode would reveal that this home is built 20 feet (6.1 m) from the river. Knowing the home’s actual distance from the river leads the insurance company to an accurate risk assessment and a correct quote. A rooftop geocoder would give the competitive edge in this case.

  3. A telecommunications company in the United States wants to understand if their customers are well covered with their new network upgrade. The company wants to ensure customers will have adequate signal strength.

    By directing their signal to structures rather than empty land or parking lots they create happier users who don’t have to wander into their backyard or parking lot to watch YouTube videos. Rooftop geocodes would be needed in this application.

How do I find Geocodes for Addresses?

This is an easy question to answer. To perform a geocode lookup, you simply need to enter a complete address into a geocoding service. You can use the hyper accurate Smarty United States Rooftop Geocoding service. You can also use our less precise ZIP+4 accurate geocode service. Either geocoder can provide you with geocodes blazing fast.

Reverse Geocoding

While geocoding helps you find latitude and longitude coordinates for an address, if you already have a geocode, you may need to transform it back into a human-readable address. After all, geocoding shouldn’t be a one way street.

This is a process called reverse geocoding and is worth learning more about. This is useful in cases where you need to identify the address of the point on a map. Such as the building address, home address or landmark.

Geocoding with the Google Geocoder

Sometimes services like Google will geocode locations that don't exist.

Places like Google and Bing usually do parcel or rooftop-level accuracy on their geocodes. Map services do this, so they can give you GPS directions to a location. It's helpful when you want to know how to drive to where you're going.

What they don't do is check for the validity of an complete address, like we do. That means if conditions aren't perfect (you entered the address incorrectly, the area isn't well mapped, etc.), Google may actually be dropping the pin on the map when it should be telling you it couldn't find what you were looking for. In short, Google doesn’t validate addresses.

So if you're counting on a mapping service to provide you with geocodes, you may find yourself requesting geocodes to a place that's no longer an active mailing address, isn't one yet, or isn't a real address at all. As many have already experienced, this is a problem even if you're looking for physical addresses rather than geocodes.

Since Smarty's first love is address standardization and address verification, it's the first thing we check. And if the place doesn't exist, we won't give you the geocodes for it.

Why Did I Care about All of This Long Enough to Read to the End?

So at the end of the day, Smarty's geocodes are hyper accurate, and they're a bunch quicker than the competition. And best of all, by combining geocoding with address validation, you can be sure the data we give you is clean and reliable.

Smarty's rooftop geocodes are offered as an upgrade to our US Street API. Our documentation contains tons of sample code to get your integration up and running fast. Try the US Rooftop Geocoding demo.

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