$api = 'http://api.map.baidu.com/shangquan/forward/?qt=sub_area_list&ext=1&level=3&areacode=1&business_flag=0';
$get_contents = file_get_contents($api);
$json_map = json_decode($get_contents, true);
$content = $json_map['content'];
$sub = $content['sub'];
$arr = [];
foreach ($sub as $vals) {
$arr[$vals['area_name']] = array_column($vals['sub'], 'area_name', 'area_code');
}
var_dump($arr);