function _cities_autocomplete($string) {
  $matches = array();
  $result = db_select('Route', 'c')
    ->fields('c', array('Location'))
    ->condition('Location', '%' . db_like($string) . '%', 'LIKE')
    ->execute();

  // save the query to matches
  foreach ($result as $row) {
    $matches[$row->Location] = check_plain($row->Location);
  }
  // Return the result to the form in json
  drupal_json_output($matches);
 // print(drupal_json_output($matches));

}

$form['op']['#autocomplete_path'] = 'cities/autocomplete';