# Calculating distance between zip codes in PHP

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Calculating distance between zip codes in PHP – Here in this article, we will share some of the most common and frequently asked about PHP problem in programming with detailed answers and code samples. There’s nothing quite so frustrating as being faced with PHP errors and being unable to figure out what is preventing your website from functioning as it should like php and mysql . If you have an existing PHP-based website or application that is experiencing performance issues, let’s get thinking about Calculating distance between zip codes in PHP.

I grabbed a database of the zip codes and their langitudes/latitudes, etc from this

ZIP, LATITUDE, LONGITUDE, CITY, STATE, COUNTY, ZIP_CLASS

The data was in a text file but I inserted it into a MySQL table. My question now is, how can i utilise the fields above to calculate the distance between two zip codes that a user can enter on the website? Working code in PHP will be appreciated

Solution :

This is mike’s answer with some annotations for the magic numbers. It seemed to work fine for me for some test data:

``````function calc_distance(\$point1, \$point2)
{

\$distance = (\$radius * pi() * sqrt(
(\$point1['lat'] - \$point2['lat'])
* (\$point1['lat'] - \$point2['lat'])
+ cos(\$point1['lat'] / \$deg_per_rad)  // Convert these to
* (\$point1['long'] - \$point2['long'])
* (\$point1['long'] - \$point2['long'])
) / 180);

return \$distance;  // Returned using the units used for \$radius.
}
``````

It can be done with just maths…

``````function calc_distance(\$point1, \$point2)
{
\$distance = (3958 * 3.1415926 * sqrt(
(\$point1['lat'] - \$point2['lat'])
* (\$point1['lat'] - \$point2['lat'])
+ cos(\$point1['lat'] / 57.29578)
* cos(\$point2['lat'] / 57.29578)
* (\$point1['long'] - \$point2['long'])
* (\$point1['long'] - \$point2['long'])
) / 180);

return \$distance;
}
``````

Check out the Haversine formula for calculating great circle distances between two points. Some more samples can be found here

Haversine formula:

• Δlat = lat2− lat1
• Δlong = long2− long1
• a = sin²(Δlat/2) + cos(lat1).cos(lat2).sin²(Δlong/2)
• c = 2.atan2(√a, √(1−a))
• d = R.c

(Note that angles need to be in radians to pass to trig functions).

You can also try hitting a web service to calc the distance. Let someone else do the heavy lifting.

https://www.zipcodeapi.com/API#distance

In your zip table you need to grab the coordinates (lat,long) for the two points for which you want to get the distance.

You can then either calculate the distance right in the SQL or with PHP. Both methods are outlined in this post:

http://dev.strategystar.net/2011/10/mysql-php-get-distance-between-two-coordinates-in-miles-kilometers/

The calculation in the example is based on the formula already discussed in this thread. It provides the radius for the earth in both miles and kilometers so it will allow you to get the distance between two points in both units.

The link above is great because the method for calculation does not include any magic numbers, just the radius of the earth!