WordPress utilities, allows the separate display of explicit levels of hierarchial taxonomies

the_terms_by_level

/**
 * Template Tag: the_terms_by_level
 *
 * Echoes the links of all the terms on the same explicit hierarchical level 
 * associated with a certain taxonomy. You should pass a separator.
 *
 * @param  $id        int     post id
 * @param  $taxonomy  string  the taxonomy
 * @param  $level     int     level of the hierarchy to echo (top level = 0)
 * @param  $sep       string  separator
 * @return void
 * @uses   get_the_terms()
 * @uses   get_ancestors()
 * @uses   get_term_link()
 */
function prefix_the_terms_by_level( $id, $taxonomy, $level, $sep ) {
  // get all the terms associated with this post
  $terms = get_the_terms( $id, $taxonomy );
  // check if there's terms in general
  if ( $terms && !is_wp_error( $terms ) ) {
    // check if level's not zero
    if ( $level != 0 ) {
      // build array that only contains terms with correct hierarchical level
      $level_terms = array_filter( $terms, function ( $term_obj ) use ( &$taxonomy, &$level ) {
        $ancestors = get_ancestors( $term_obj->term_id, $taxonomy );
        if ( count( $ancestors ) == $level ) {
          return true;
        } else {
          return false;
        }
      });
      // check that it's not empty
      if ( !empty( $level_terms ) ) {
        // get last key of array
        $last_key = array_search( end( $level_terms ), $level_terms );
        // build $links string
        $links = '';
        foreach ( $level_terms as $key => $level_term ) {
          $links .= '<a href="' . get_term_link( $level_term ) . '" rel="tag">' . $level_term->name . '</a>';
          if ( !( $key == $last_key ) ) {
            $links .= $sep;
          }
        }
        echo $links;
      // else echo that
      } else {
        echo 'n/a';
      }
    // else show top level domains
    } else {
      // loop trough the terms
      foreach ( $terms as $key => $term ) {
        // if term is top level, write in separate array
        if ( $term->parent == 0 ) {
          $toplevel_terms[] = $term;
        }
      }
      if ( !empty( $toplevel_terms ) ) {
        // get the last key in the array (for the separator)
        $last_key = array_search( end( $toplevel_terms ), $toplevel_terms );
        // links string
        $links = '';
        // loop through toplevel array...
        foreach ( $toplevel_terms as $key => $toplevel_term ) {
          // and build $links string
          $links .= '<a href="' . get_term_link( $toplevel_term ) . '" rel="tag">' . $toplevel_term->name . '</a>';
          // if not the last term, add separator
          if ( ! ( $key == $last_key ) ) {
            $links .= $sep;
          }
        }
        echo $links;
      } else {
        echo 'n/a';
      }
    }
  // if there's no terms at all echo that there's none
  } else {
    echo 'n/a';
  }
}

the_toplevel_terms

/**
 * Template Tag: the_toplevel_terms
 *
 * Echo out all the top level terms of an hierarchical taxonomy,
 * based on id and taxonomy. You should pass a separator.
 *
 * @param  $id        int     id of the post
 * @param  $sep       string  separator in between term links
 * @param  $taxonomy  string  the taxonomy in question
 * @return void
 * @uses   get_the_terms()
 * @uses   get_term_link()
 */
function prefix_the_toplevel_terms( $id, $taxonomy, $sep ) {
  // get associated terms based on taxonomy
  $terms = get_the_terms( $id, $taxonomy );
  // loop trough the terms
  foreach ( $terms as $key => $term ) {
    // if term is top level, write in separate array
    if ( $term->parent == 0 ) {
      $toplevel_terms[] = $term;
    }
  }
  if ( !empty( $toplevel_terms ) ) {
    // get the last key in the array (for the separator)
    $last_key = array_search( end( $toplevel_terms ), $toplevel_terms );
    // links string
    $links = '';
    // loop through toplevel array...
    foreach ( $toplevel_terms as $key => $toplevel_term ) {
      // and build $links string
      $links .= '<a href="' . get_term_link( $toplevel_term ) . '" rel="tag">' . $toplevel_term->name . '</a>';
      // if not the last term, add separator
      if ( ! ( $key == $last_key ) ) {
        $links .= $sep;
      }
    }
    echo $links;
  } else {
    echo 'n/a';
  }
}