Sometimes you just need to know what country your site
visitors are coming from—for example, if you’re trying to implement geo-targeted advertising.
That’s where a tool like MaxMind’s GeoIP comes in—it lets you easily extract
geographic data from your visitor’s IP address.

MaxMind makes available both commercial and free databases;
the commercial ones are extremely precise and can get as fine-grained as the
user’s city, while the free version can only identify the country of origin. We’ll
use the free version in this article. If you need more detailed information,
such as the remote client’s city and state of origin, you will need to purchase
a more detailed database from MaxMind.

Getting started

To use it, you’ll have to first download
the GeoIP Free Country
file and extract it into a directory in your Web
server. Then you’ll have to pick which language API to use with the database
file. For simplicity, we’re going to use the pure
PHP
version because it doesn’t require any additional configuration or
Apache modules. Remember to read the license
terms
before installing these on your Web site to ensure you are in
compliance.

The code in Listing A demonstrates the basics of using the module
(geoip.inc) to access the GeoIP Free Country database (GeoIP.dat). The example
assumes both the PHP include and the country database file
are in the same directory as the PHP file itself. You’ll have to change
the paths as needed if this is not the case in your installation.

The sample code is pretty straightforward. After including
the GeoIP PHP function library, the first step is to open the GeoIP database
file with the geoip_open() function. This function
accepts two arguments: the path to the database file and the type of database.

We then use the handle returned by the call to geoip_open() to obtain the two-letter country code and
human-friendly name corresponding to the given IP address, via the
geoip_country_code_by_addr() and geoip_country_code_by_name() functions,
respectively. Both functions accept two arguments: the handle returned by
geoip_open() and the IP address to resolve.

Once the required information is obtained, we close the database
file with a call to geoip_close(). Simple
as that.

Using the geographic data

Now, what to do with this geographic knowledge? Well, one
good use for geographic data is to target users with ads tailored to their
country. Here’s a simple example in PHP that uses a MySQL database to deliver geo-targeted
ads.