Zip Code to City/State and vice-versa in a database?

Question

I'm new to SQL and relational databases and I have what I would imagine is a common problem.

I'm making a website and when each user submits a post they have to provide a location in either a zip code or a City/State.

What is the best practice for handling this? Do I simply create a Zip Code and City and State table and query against them or are there ready made solutions for handling this?

I'm using SQL Server 2005 if it makes a difference.

I need to be able to retrieve a zip code given a city/state or I need to be able to spit out the city state given a zip code.

Answer 1

You have a couple options. You can buy a bulk zip-code library from somebody which will list zip codes, cities, counties, etc. by state, or you can pay someone to access a web service which will perform the same function on a more granular level.

Your best bet would be to go with the zip-code library option, as it'll cost you less than the web service and will provide better performance. How you query or pre-process this library is up to you. You mention SQL Server, so you'd probably want State, Zipcode, and City tables, and include the relevant relationships between them. You'll also need to have provisions for cities that span multiple zipcodes, or for zipcodes that have multiple cities - but none of these issues are insurmountable.

As far as dealing with the vagarities of user input, you may consider enlisting the help of an address validation web service, although most of them require a full shipping address in order to validate.

Edit: looks like there's a SourceForge project offering free zip-code data, including lat/lon data, etc. Not sure how correct or current it is.

Edit 2: After some cursory looking on that SourceForge project's site it looks like this is a dead project. If you use this data, you'll need to provide some allowance for zipcodes / cities that don't exist in your database. Purchased bulk libraries usually come with some sort of guarantee of updates, or a pricing plan for updates, etc., and are probably more reliable.

Answer 2

My understanding is that the USPS web API is free to use, but requires permission that depends on a number of factors, including the nature of the program that will be using it and the reason you need the data.

If you qualify to use it, this would presumably be the most accurate source for the information you need.

Answer 3

Have a ZipCode table that is related to a CityState table. Some zip codes have multiple cities associated with them, so you may need to have the interface let the user select from the city they want or let them override the default.

I use the paid service from ZipInfo.com since I needed additional information such as lat/long, zip type and county. Zip codes also change several times as year as new zip codes are added or merged with others, so you will need to update your data a few times a year to stay consistent.

Answer 4

Depending on the details of what you're building, Yelp has a free neighborhoods API that may be able to get you what you need. Be sure to check their Terms of Use and stuff to make sure you stay in compliance.

I know this isn't a db centric answer, but what you're doing may not be best handled in the database itself.

Answer 5

Not sure I understand the question. Do you need to allow either and, later, return both?

You'll have to be careful, even with a zip/city database that can be purchased, since some cities span multiple zips, so you can't always "calculate" in that direction. Similar issue in the opposite direction.

Answer 6

There are libraries that you can buy and import that aren't that expensive. Your problem with them is going to be that you will have an ongoing maintenance cost with it (not a lot). Zip codes change all the time, meaning that in 6 mos or so, your data will be slightly out of date. You might want to look at interfacing with a service like google maps. Here we use a hybrid approach. We spend the amount of the money for updates to the data every 6 months, and if the zip code isn't in the table we verify it against google maps to make sure that information entered is still valid and it just hasn't been entered into our system. If it is valid, we update the system, if not we let the user know that a mistake was made.

Another option would be to ping the USPS website. I believe they have a city/state look up page by zipcode.

Answer 7

I got that beat. Here's a free one (zipped, csv):

Hosted At maphacks.com

Headers are zip,city,state,latitude,longitude,timezone,dst

Now, your potential loss is that you aren't paying for updates (which can bite you in the end, but they try to keep it somewhat updated)

Answer 8

There are many free geo-coding webservices where you can get a zip from a city-state, and vice-versa. Take a look at the GeoNames webservice. You could do something like check your db, and then if what you are looking for is not there, grab it from the webservice and add it.

Answer 9

If the reason for the lookup is the user's convenience, here's an alternate approach that doesn't require licensing any third-party databases:

Just lookup the city/state from your existing name/address table, provided the zip code matches. If somebody has previously made an entry for that zip code, then you'll find the city and state from that entry. IF no previous entry exists, then worst case the user has to entry in the city and state.

This solution assumes your need is for convenience for the user. If you are more concerned about accurate validation of city, state, zip codes then you're better off licensing a verified database.

Answer 10

Free zip code database located at:

http://www.populardata.com

Answer 11

As previously mentioned, PopularData.com provides a free CSV of U.S. ZIP code data.

I generated a SQL script for populating a SQL Server 2005 table with the PopularData.com ZIP code data.

You can use this table to do ZIP-to-City/State or City/State-to-ZIP lookups.

The usual caveat applies here: you get what you pay for. If you need assurance that the data are up-to-date and valid, go with a commercial solution.

Answer 12

Cheap USPS data is at http://semaphorecorp.com

For the pitfalls of only validating city-ZIP correspondence without considering the address, see http://semaphorecorp.com/cgi/zip5.html