<?php
if(@$_POST['map_x'])
{    
    $width  = 310;
    $height = 155;
    $values = getlocationcoords_inv($_POST['map_x'],$_POST['map_y'], $width,$height); 
}

function getlocationcoords_inv($x,$y, $width,$height) 
{
    $lat = ((($y / $height) * 180) - 90) * -1;
    $lon =(($x / $width) * 360) - 180;
    return array($lat,$lon);
}
?>
<input name="map" type="image" id="map" src="pic/earth.jpg" width="310" height="155" border="0">

Longitude: <?=@$values[1];?><br>
Latitude: <?=@$values[0];?><br>

?>