$liste_regions = array (
	"Alsace" => array(67,68),
	"Aquitaine" => array(24,33,40,47,64),
	"Auvergne" => array ("03",15,43,63),
	"Basse-Normandie" => array (14,50,61),
	"Bourgogne" => array (21,58,71,89),
	"Bretagne" => array (22,29,35,56),
	"Centre" => array (18,28,36,37,41,45),
	"Champagne-Ardenne" => array ("08",10,51,52),
	"Corse" => array(20),
	"DOM-TOM" => array(97),
	"Franche-Comté" => array (25,39,70,90),
	"Haute-Normandie" => array (27,76),
	"Ile de France" => array(75,77,78,91,92,93,94,95),
	"Languedoc-Roussillon" => array(11,30,34,48,66),
	"Limousin" => array(19,23,87),
	"Lorraine" => array (54,55,57,88),
	"Midi-Pyrénées" => array("09",12,31,32,46,65,81,82),
	"Nord / Pas-de-Calais" => array(59,62),
	"Pays de la Loire" => array (44,49,53,72,85),
	"Picardie" => array ("02",60,80),
	"Poitou-Charentes" => array (16,17,79,86),
	"PACA" => array("04","05","06",13,83,84),
	"Rhône-Alpes" => array ("01","07",26,38,42,69,73,74)
);

// Renvoie la région à partir du code postal ou du numéro de département
function region($codepostal) 
{
		global $liste_regions;
		$departement = substr($codepostal,0,2);
		
		foreach($liste_regions as $region => $liste_dep) 
		{
			if (in_array($departement, $liste_dep))
			{
				return $region;
			}
		}		
}
print region(35170); 
// Renvoie Bretagne

Trouver la région à laquelle appartient un département

PHP