gistfile1.php

<?php
/**
 * Returns all the layers in the tile service.
 *
 * @return array
 */
function simplegeo_tileservice_get_layers() {
  static $layers;
  $cache_key = 'simplegeo_tileservice:layers';

  if (!$layers && ($cache = cache_get($cache_key)) && isset($cache->data)) {
    $layers = $cache->data;
  }

  if (!$layers) {
    $layers = module_invoke_all('simplegeo_tileservice_layers');
    drupal_alter('simplegeo_tileservice_layers', $layers);

    // Get rid of layers with invalid types
    $types = simplegeo_tileservice_get_layer_types();
    foreach ($layers as $name => $def) {
      if (!isset($def['type']) || !isset($types[$def['type']])) {
        unset($types[$name]);
      }
    }
    cache_set($cache_key, $layers);
  }

  return $layers;
}