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Here in Britain people can license the Ordnance Survey's AddressBase product, which provides a list of almost all the country's addresses, along with individually surveyed building locations. Like all geodata products it's got some errors and omissions, but it's generally good - even in remote areas. This is useful for address suggestion and geocoding (some of the major parts of what I want to achieve).

I'd like to broaden my knowledge beyond just the UK. What's the best data available for the United States, and how good is it?

I'm aware that the USPS has a "zip+4" file that contains 30 million addresses (presumably not a full list of addresses in a country of 300 million people); that Navteq's map data contains street number ranges (in the UK their accuracy is OK but not the best); that Google have a geocoding API (I would prefer a database rather than an API); and that TIGER data contains some address information (I haven't fully investigated this - is it any good?). Should I be looking at one of these options in more detail, or are there other sources I've missed?

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It might help if you can say exactly what you need the data for. You mention "address suggestion and geocoding", but don't actually say this is what (or all) you are looking for. – BradHards Dec 10 '13 at 23:59
I want the data for address suggestion, validation and geocoding. – GeoDave Dec 11 '13 at 0:03

2 Answers 2

up vote 5 down vote accepted

I used to work at SmartyStreets, a licensed CASS™ vendor of USPS address data. What you want to do sounds exactly like what they do.

The USPS ZIP+4 file is available from many sellers, but you're right: it only contains about 30-40 million records. We sometimes called it the "ranges" file because it contains address data at a range level only. In other words, it provides street names in cities/states with a range of primary numbers, say, 100-8000, where, in rural areas, only a few of those numbers actually exist.

The full USPS address database comes to licensed CASS™ vendors and the like, which has some added expenses and certification tests.

USPS data contains no geocoding or geolocation data. The USPS' primary concern is mailing: routing and delivering mail. Any correlation between address data such as ZIP codes and actual coordinates or physical proximity is entirely coincidental.

The USPS data is considered a private source. It is expensive to obtain and license, and typically requires conforming to rigorous terms and quality testing (like CASS™ Certification.)

TIGER data is a freely available, public data source. However, it does not correlate to USPS data, except for ZCTAs which were created several years ago. The only way to update that data, as I understand, is to start with the old data and apply all the delta files between now and then.

TIGER geocoding data is not very accurate and is often outdated. (At SmartyStreets, we've been bitten by this before.) Further, converting Census Bureau data into address coordinates is a slow, tedious process.

If you're doing precision skydiving based on TIGER data, you should verify the coordinates yourself. That's how companies like Google, which excellent geocoding capabilities, have amassed much of their data: driving vehicles on all the streets to manually collect map and coordinate data, then aggregate theirs with public sources, to produce very high-quality, competitive, and super-expensive results.

To compensate for poor quality public sources, we've worked with private geocoding services to obtain much better data (rolling out over the next few weeks, in fact).

As for database vs. API -- good luck. The good data is limited to licensed vendors. Google and the like don't hand out their databases at all.

In the end, even though these services all package and distribute their products differently, they nearly all trace back to the same data sources.

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Thanks - that's really helpful. None of the CASS-certified vendors I've seen offer address suggestion - it that a requirement for getting the USPS address or something? One of the things I don't like about APIs is when they say "no match" for a street you know exists, and with no access to the data you have no way of working out why. – GeoDave Dec 12 '13 at 8:42
@GeoDave What do you mean by address suggestion exactly? I bet there are at least a couple. – Matt Dec 12 '13 at 16:10
I've used SmartyStreets previously and as a data geek, thoroughly recommend it! – Elliott Dec 12 '13 at 20:54
@Matt Autocomplete / near match suggestions. I thought smartystreets didn't do it, but I guess the address I was testing with ("708 Lynhaven Dr, Lenoir, NC") just wasn't in your data. Is that backed by the USPS private data? – GeoDave Dec 13 '13 at 19:29
@GeoDave Ah. Yes, it is. Notice that the address validates. It's also in the autocomplete, but you don't see it once you type "Dr" followed by the city name because it is a "St" in Lenoir, not a "Dr". Autocomplete does not override what you type in while it gives suggestions, since you know your address better than it does: but validating the address will resolve any discrepancies. That's the difference between suggestion and validation (in our book). – Matt Dec 13 '13 at 19:41

Historically TeleAtlas had the best data. Many commercial sources use them and they were provider to the USPS. The cost would be prohibitive. Tiger is free. TA is now TomTom and where they improved data in major urban areas the accuracy would typicalLy be in the 95% to 98% range. The sources would be municipal data, banking industry parcel maps, postal service, tiger, online real estate sites, etc.

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