diff --git a/code/map_data_cache.js b/code/map_data_cache.js
index d6868557..a03e33de 100644
--- a/code/map_data_cache.js
+++ b/code/map_data_cache.js
@@ -26,15 +26,19 @@ window.DataCache = function() {
 
 }
 
-window.DataCache.prototype.store = function(qk,data,date) {
+window.DataCache.prototype.store = function(qk,data,freshTime) {
   // fixme? common behaviour for objects is that properties are kept in the order they're added
   // this is handy, as it allows easy retrieval of the oldest entries for expiring
   // however, this is not guaranteed by the standards, but all our supported browsers work this way
 
   delete this._cache[qk];
 
-  if (date === undefined) date = new Date();
-  this._cache[qk] = { time: date.getTime(), data: data };
+  var time = new Date().getTime();
+
+  if (freshTime===undefined) freshTime = this.REQUEST_CACHE_FRESH_AGE*1000;
+  var expire = time + freshTime;
+
+  this._cache[qk] = { time: time, expire: expire data: data };
 }
 
 window.DataCache.prototype.get = function(qk) {
@@ -50,8 +54,8 @@ window.DataCache.prototype.getTime = function(qk) {
 window.DataCache.prototype.isFresh = function(qk) {
   if (qk in this._cache) {
     var d = new Date();
-    var t = d.getTime() - this.REQUEST_CACHE_FRESH_AGE*1000;
-    if (this._cache[qk].time >= t) return true;
+    var t = d.getTime();
+    if (this._cache[qk].expire >= t) return true;
     else return false;
   }