Compute the great-circle distance between two latitude/longitude points using the haversine formula. Returns kilometers; multiply by 0.621 for miles. Useful for "stores near me" features.
PHP
<?php
function haversineKm(float $lat1, float $lng1, float $lat2, float $lng2): float {
$R = 6371.0; // Earth radius in km
$dLat = deg2rad($lat2 - $lat1);
$dLng = deg2rad($lng2 - $lng1);
$a = sin($dLat / 2) ** 2
+ cos(deg2rad($lat1)) * cos(deg2rad($lat2)) * sin($dLng / 2) ** 2;
return 2 * $R * atan2(sqrt($a), sqrt(1 - $a));
}
// Distance from Austin to San Francisco
printf("%.0f km\n", haversineKm(30.2672, -97.7431, 37.7749, -122.4194)); // ~2425 kmSave your own code snippets
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