<?php
$lat = 48.8583;
$lon = 2.2945;
$z = 18;
$baseUrl = 'http://nominatim.openstreetmap.org/reverse?format=json&';
$data = file_get_contents( "{$baseUrl}lat={$lat}&lon={$lon}&zoom={$z}" );
$data = json_decode( $data );
echo $data->display_name, "\n";
print_r( $data );
?>
Output
http://wiki.openstreetmap.org/wiki/Nominatim