api for zip +4 from an address - geolocation

Question

What's the best api/resource to get a zip +4 from an address?
I don't want something that needs to be downloaded and updated from time to time; I want one that's updated automagically.
The goal is to look up state and federal officials without getting "duplicate" positions.

Answer 1

have you tried Google Maps JavaScript API V3
UPDATED:
in responce to your comment
this is easy as count 1, 2 , 3 ;)
take a look at this:
http://maps.google.com/maps/api/geocode/json?address=Winnetka&sensor=false
you need to looking for google map geocoding service! ( Viewport Biasing )
http://code.google.com/intl/it-IT/apis/maps/documentation/geocoding/
example code would be:
using jQuery
$(function() {
$.getJSON("http://maps.google.com/maps/api/geocode/json?address=Winnetka&sensor=false",
function(data) {
var zip_code = data.results[0].long_name;
alert(zip_code);
});
});

Answer 2

Yahoo has a zip + 4 in thier API, limit 5000 request per day.
Yahoo GeoCoding

Answer 3

The USPS has an API for finding/checking zip codes (among other things).
http://www.usps.com/webtools/address.htm

Answer 4

I've used Endicia at past jobs. It is a network HTTP-based API. (I can't remember if it was SOAP or REST.)

Answer 5

Apple provide brilliant facility to get zip+4code from lattitude and longitude with reverse geocoder -
- (void)getPlaceMarkInfo
{
CLLocationCoordinate2D coordinate;
coordinate.latitude = your lattitude;
coordinate.longitude = your longitude;
MKReverseGeocoder *RevGeoCoder = [[MKReverseGeocoder alloc] initWithCoordinate:coordinate];
RevGeoCoder.delegate = self;
[RevGeoCoder start];
}
#pragma mark MKReverseGeocoderDelegate:
- (void)reverseGeocoder:(MKReverseGeocoder *)geocoder didFindPlacemark:(MKPlacemark *)placemark
{
NSLog(#"YOUR STATE IS - %#",[placemark.addressDictionary valueForKey:#"State"]);
NSDictionary *dictAddress = placemark.addressDictionary;
NSString *strZipPlus4Code = [NSString
stringWithFormat:#"%#-%#",[dictAddress valueForKey:#"ZIP"],
[dictAddress valueForKey:#"PostCodeExtension"]];
strStateName = [placemark.addressDictionary valueForKey:#"State"];
}
- (void)reverseGeocoder:(MKReverseGeocoder *)geocoder didFailWithError:(NSError *)error
{
NSLog(#"REVERSE GEOCODER FAILED");
}

Answer 6

Previous answers have included some really good information, most importantly:
USPS API can only be used if you're shipping through USPS (from their terms of service: "User agrees to use the USPS Web site, APIs and USPS data to facilitate USPS shipping transactions only.")
ZIP Codes are adjusted/updated fairly frequently, so it would be important to have the most current data. (More info about how often to re-validate your addresses here)
You also said you want something that doesn't need to be installed and kept updated.
With those qualifications in mind, I would suggest LiveAddress API. It's a cloud-based, automatically updated API that returns, among over 40 other datapoints, ZIP+4 data on your addresses. It can handle thousands of addresses per second, so it's super-fast and easy to use. If you have a list of address you want to work though (rather than one at a time), you might want LiveAddress for Lists, which lets you upload and process a whole list at once.
Disclosure: I work at SmartyStreets, the company that provides LiveAddress.

Answer 7

In reference of Yahoo BOSS GEO Api:
http://yboss.yahooapis.com/geo/placefinder?location=170+South+Market+St.,+San+Jose,+CA
Make a GET request with following authorization HEADER
Example of using OAuth in HTTP Header:
Authorization: OAuth realm="http://yboss.yahooapis.com/",oauth_consumer_key="dj0yJmk9QnFUYVRUSWtRZEhsJmQ9WVdrOVFrYzFja2x4TkdNbWNHbzlNVEExTWpFMk1ESTJNZy0tJnM9Y29uc3VtZXJzZWNyZXQmeD1lNA--",oauth_nonce="ZDQDDVLFCWKCZ0BD",oauth_signature_method="HMAC-SHA1",oauth_timestamp=" 1367827192",oauth_version="1.0",oauth_signature="phP2dNiCmvwpK4M6G%2F85KnnvTXo%3D"
where:
Authentication for BOSS Geo queries requires OAuth information in the HTTP header OR through parameters in the GET request. There are six elements that are required for authorization:
oauth_version=1.0 – The standard of OAuth supported by BOSS Geo.
oauth_timestamp= – The timestamp is expressed in the number of seconds since January 1, 1970 00:00:00 GMT. The timestamp value MUST be a positive integer and MUST be equal to or greater than the timestamp used in previous requests. The timestamp can be reused for up to 5 minutes. Important: After 5 minutes a fresh timestamp must be supplied.
oauth_nonce – is a random string, uniquely generated for all requests for a specific timestamp. This helps verify that a request has never been made before and helps prevent replay attacks when requests are made over a non-secure channel (such as HTTP).
oauth_consumer_key= – obtained from YDN during the BOSS project registration process. This is unique to the developer. Please follow the directions on the displayed key page and copy the entire key from YDN. If you do not copy the entire key, this results in a "Consumer Key rejected" error.
oauth_signature_method=HMAC-SHA1 – (specific algorithm used for BOSS OAuth calls).
oauth_signature – can be generated by an OAuth library. A list of supported OAuth libraries is available here: http://oauth.net/code. Over a dozen languages are supported.
You will get zip+4 code in Response under "postalcode" key.