zip+4 to lat/lon? Where? & precision necessary?

December 12, 2006 12:04 PM

I want a free-as-in-beer way to put in a ZIP+4 postal code and get back a latitude and longitude. Unless that's more precision than I need for terrestrial astronomy.

Do I need that precise a translation for an Earth-based astronomy program like Cartes du Ceil, or will a simple five-digit ZIP code do me? I see from previous posts that I could spend a while researching that question, but I just want a quick translation of my posit.

posted by pax digita to travel & transportation (6 comments total)

http://geocoder.us/
posted by GuyZero at 12:11 PM on December 12, 2006

If you want super precision, you can get your lat/long by finding your location on a map and looking at the URL, at maps.google.com (or probably any other on-line map thingy).
posted by Brian James at 12:52 PM on December 12, 2006

Woops, I was thinking of Google Earth. Same idea.
posted by Brian James at 12:54 PM on December 12, 2006

ZIP+4 is not great for this. Most people don't know their +4, so they have to look it up, and the address they give to look it up is actually more precise than the ZIP+4 would be. (Since ZIP+4 is usually a range of houses on a given street, not a square area.) So you're throwing away data for no reason.

Plus, the Google Maps API has a street address geocoder now. It's relatively new, and as free as the other uses of the API.
posted by smackfu at 1:09 PM on December 12, 2006

As others have pointed out, Google maps is better for this, but I did want to address this question:

Do I need that precise a translation for an Earth-based astronomy program like Cartes du Ceil

Probably not, but it depends on your rig.

Say the difference between Zip+4 locations averages a mile, and in reality, its usually much less. For most of the USA a distance of 1 mile is the same order of magnitude as 1 minute of arc. It's hard to acheive that kind of repeatability with a portable rig on each setup. Most computer-controlled positioning software deals with this by asking you to align your telescope to two or more guide stars on initialization.

1 minute of arc also corresponds to a time difference of about 4 seconds. For comparison purposes, most amateur star-hopping probably is done with a field of view between 0.1 and 1.0 degrees, or 6 to 60 minutes of arc. So, unless your observations are via a pier-mounted fixed rig with precision positioning hardware and an atomic time source, yeah, it's probably overkill.

GPS is even better than Google maps (assuming you have one,) since it's both a precision location and time source.
posted by Opposite George at 2:08 PM on December 12, 2006

This may not be accurate enough, but RustyBrooks posted a ZIP code database that contains the (center) lat/long of every ZIP code in the U.S.

It's my understanding that ZIP+4 changes on a regular basis, so it's probably not going to be as accurate as you think. Depending on your purposes, ZIP alone may be close enough (it'll be accurate to within a couple miles in more densely populated areas, at least).
posted by neckro23 at 4:33 PM on December 12, 2006