Counting post fields

You can do custom query loop for that particular meta box for an empty value. Something along the lines of

$check_city_value = get_post_meta($post->ID, 'city_box'); ?>
if (empty($check_city_value)) {
    echo '$check_city_value is either 0, empty, or not set';
}

You would have to loop through all the posts to do this and for multiple meta box checking it might just be better to use a more direct database query using $wpdb ,
http://codex.wordpress.org/Function_Reference/wpdb_Class