Your code seems right, check if you have fopen wrappers enabled (allow_url_fopen = On on php.ini)
Also, as mentioned by other answers, you should provide a properly encoded URI or encode it using urlencode() function. You should also check if there is any error fetching the XML string and if there is any parsing error, which you can output using libxml_get_errors() as follows:
<?php
if (($response_xml_data = file_get_contents($map_url))===false){
echo "Error fetching XML\n";
} else {
libxml_use_internal_errors(true);
$data = simplexml_load_string($response_xml_data);
if (!$data) {
echo "Error loading XML\n";
foreach(libxml_get_errors() as $error) {
echo "\t", $error->message;
}
} else {
print_r($data);
}
}
?>
If the problem is you can't fetch the XML code maybe it's because you need to include some custom headers in your request, check how to use stream_context_create() to create a custom stream context for use when calling file_get_contents() on example 4 at http://php.net/manual/en/function.file-get-contents.php