我联系了Scribu，因为他的Query Multiple Taxonomies插件做了我想做的事情，他为我指明了正确的方向。我（在我的开发环境中）已经做到了这一点，所以我想就是这样了。（Scribu将这些函数作为一个类的一部分拆分为两个函数-我相信这是一种“优雅”（非故意的双关语）的方式-但这是内联的：（在这里发布，以防对其他人有帮助…）

//building this as if we were going to look for
//posts that have been categorized with this service
$tempargs = array(\'post_type\' => \'vendors\',
        \'tax_query\' => array(array(
                    \'taxonomy\' => \'service\',
                    \'field\' => \'id\',
                    \'terms\' => intval($_GET[\'srv\'])
                ))
            );
$args = array_merge( $tempargs, array(
        \'fields\' => \'ids\',
        \'nopaging\' => true,
        \'no_found_rows\' => true,
        \'ignore_sticky_post\' => true,
        \'cache_results\' => false,
) );
$query = new WP_Query;
$filtered_ids = $query->query( $args );
//now getting the list of location terms that have posts in this service
$locationsWdups = wp_get_object_terms( $filtered_ids, \'location\' ); 
//the above will include duplicate locations so we\'ll combine them
//into one array below
$locations = array();
foreach ( $locationsWdups as $singloc )
     $locations[ $singloc->term_id ] = $singloc;    

（如果我遗漏了什么或做得不正确，请纠正我）