Comments on: Where to get postcodes and map them to distances?

Question: Where to get postcodes and map them to distances?

reklaw — Tue, 15 Mar 2005 05:16:55 -0800

I'd like to store people's postcodes and work out distances between them. I think I need a postcode-to-coordinates database, and then a way of working out the distances...

So, two questions really:

1. Where can I get a database mapping postcodes to latitude and longitude (or some other better co-ordinate system)? Free is the best price, but not essential, and the UK is the most important place to cover, but as many as possible would be nice.
2. Once I had such a thing, how would I go about working out the distances between postcodes with it?

PS. This is for a free project, not a business or my job or anything.

By: tomierna

tomierna — Tue, 15 Mar 2005 06:08:58 -0800

If you have lat/long, some pythagorean love should fix you right up. Two points on a grid, draw a hypotenuse.

It won't be perfectly accurate due to elevation and the earth's curvature, but it should be damn close.

I remember we found a free zip-lat/long db on the intarweb in about 1998, but I don't remember where. Try the USPS or USGS.

By: chota

chota — Tue, 15 Mar 2005 06:09:23 -0800

Sorry, can't help with the first part, but the answer to the second part of your question is:

Cartesian Coordinates.

The system of latitude and longitude is really just a graph that's set up like a simple piece of graph paper in a high school algebra/trig class.

Most people don't like learning about applied math though, so here's a link to a javascript page that will calculate the distance for you (in miles, km, and leagues):

Surface Distance Between Two Points of Latitude and Longitude

By: ralawrence

ralawrence — Tue, 15 Mar 2005 06:24:20 -0800

This site gives you a csv file of postcodes and their latitude and longitude.

By: ralawrence

ralawrence — Tue, 15 Mar 2005 06:28:12 -0800

Oh and this site gives you ASP code to work out the distance. ASP is essentially a basic-like language and so it's very easy to understand what they're doing and convert it into your choice of language.

Hmm, I think I might have a go at doing it myself.

By: RustyBrooks

RustyBrooks — Tue, 15 Mar 2005 07:15:41 -0800

I have a zipcode database in a format suitable for reading into a database, and I also have the math pretty much worked out, and code for it. It's in a language most people don't use (tcl) but I could probably throw up a web page with the file, some info on the math, etc, if anyone is interested.

By: RustyBrooks

RustyBrooks — Tue, 15 Mar 2005 07:50:12 -0800

OK, I threw something quickly together. Try this out:
My zipcode thingy.

It has a CSV file, suitable for loading into excel or a database, the code (which is pretty well commented), and a quick example where you can look up some zip codes and find out how far away you are from me.

Which reminds me -- mathowie must have something like this since he has something that shows how far other users are from you.

By: odinsdream

odinsdream — Tue, 15 Mar 2005 08:10:51 -0800

If I'm not mistaken, I believe the metafilter version simply does things numerically. Distance is only involved in that postal codes near eachother are usually numerically close. So, since I'm 27104, I'm "near" 27100-27110, but that didn't require figuring out any physical distances.

By: RustyBrooks

RustyBrooks — Tue, 15 Mar 2005 08:29:46 -0800

Hmm. I suppose that's possible. He's welcome to steal my zipcodes if he feels like it.

By: RustyBrooks

RustyBrooks — Tue, 15 Mar 2005 08:30:16 -0800

Oh and now that I read the question, I've no idea if my database covers the UK or not. Probably not.

By: neckro23

neckro23 — Tue, 15 Mar 2005 08:44:44 -0800

Rusty: It looks like the database only covers the US. However, I'm personally glad you posted it because I was looking for something exactly like that, so thanks!

By: bachelor#3

bachelor#3 — Tue, 15 Mar 2005 13:45:07 -0800

According to this page, the process is called georeferencing or geocoding. This might come in handy for subsequent google sessions...