MaxMind Free GeoLite City DB Unreliable?

Question

I am attempting to use MaxMind's GeoLite City database in to convert ip addresses to lat/long combinations and find the closest city based on the coordinates.

First I convert the ip to an int using (this is Java):

String ip = "24.123.181.38";
private int ipToInt(String ip) {
    String[] nums = ip.split("\\.");
    double a = Double.valueOf(nums[0]);
    double b = Double.valueOf(nums[1]);
    double c = Double.valueOf(nums[2]);
    double d = Double.valueOf(nums[3]);
    double answer = (a*Math.pow(256, 3))+(b*Math.pow(256, 2))+(c*256)+d;
    return (int) answer; 
}
//Returns 410760486

I verified I am performing the calculation properly using one of the many online calulators for ip to integer conversion.

I then use a MySQL query to get the lat/long and perform the distance check. This distance check seems to work well for other postal code stuff I do.

SET @ip := 410760486, @dist := 10;
SELECT @orig_lat := ip_locations_latitude, @orig_lon := ip_locations_longitude FROM ip_locations WHERE @ip BETWEEN ip_locations_start_ip AND ip_locations_end_ip;

SELECT *,
(3956 * 2 * ASIN(SQRT( POWER(SIN((@orig_lat - abs(latitude)) * pi()/180 / 2),2) + COS(@orig_lat * pi()/180 ) * COS(abs(latitude) *  pi()/180) * POWER(SIN((@orig_lon - longitude) *  pi()/180 / 2), 2) )))
AS distance
FROM geolite_locations
HAVING distance < @dist ORDER BY distance LIMIT 0, 1;

I am testing using an IP address in Charlotte, North Carolina. The result returns Concord, NC (I live in this region and Concord is very close, but not the correct city none the less). I have tested on other ips in Texas, California, Washington etc and all but a few seem to return similar results...close, but not exact.

Max Minds website states that the paid version is more accurate than the free version, but should it be this different? Or am I doing something wrong in my querying? Testing the ip on Max Minds website using their paid versions online demo returns the correct cities, but I can't test their free database. If the free version is simply unusably inaccurate I have nothing against paying for the database but i'd rather not do that without having verified the data is a lot more accurate.

On a side note, please no suggestions for API's. I'd prefer to query the data locally because the project its involved in will be hitting the database quite frequently and an API call would make it too slow.

Answer 1

Typically the IP location is the location of the internet service provider who is providing the service to the customer. So in your case, your ISP may well be based in Concord, NC, so the database result is correct. In general, this type of location does not provide pin point accuracy, unless combined with other information.