Modify Info Window Contents for Posts Using Hook

gistfile1.txt

add_filter('wpgmp_infowindow_post_message', 'wpgmp_infowindow_post_message',1,2 );

function wpgmp_infowindow_post_message($message,$map) {
	global $post;
  	//This will apply for map id 1.
	if( $post->ID == 1) {
		$message = "<h1>{marker_title}</h1>";
  	}

  	if( $post->ID == 107) {
		$message = "<h1>{marker_title}</h1><p>{marker_address}</p>";
  	}

	return $message;

}

where I put that code..?

Please don't torture people with that rubbish!
When calling $post->ID, you get the id of the current page or post, where map is embedded.
Instead why not using the $map-object with $map->map_id ?