diff --git a/code/data_cache.js b/code/data_cache.js
index f7c2c443..2cf72cfc 100644
--- a/code/data_cache.js
+++ b/code/data_cache.js
@@ -4,17 +4,22 @@
 window.DataCache = function() {
   this.REQUEST_CACHE_FRESH_AGE = 3*60;  // if younger than this, use data in the cache rather than fetching from the server
 
-  this.REQUEST_CACHE_MAX_AGE = 15*60;  // maximum cache age. entries are deleted from the cache after this time
+  this.REQUEST_CACHE_MAX_AGE = 5*60;  // maximum cache age. entries are deleted from the cache after this time
 
+  //NOTE: characters are 16 bits (ECMAScript standard), so divide byte size by two for correct limit
   if (L.Browser.mobile) {
     // on mobile devices, smaller cache size
-    this.REQUEST_CACHE_MAX_SIZE = 300;  // if more than this many entries, expire early
+    this.REQUEST_CACHE_MAX_ITEMS = 300;  // if more than this many entries, expire early
+    this.REQUEST_CACHE_MAX_CHARS = 5000000/2; // or more than this total size
   } else {
     // but on desktop, allow more
-    this.REQUEST_CACHE_MAX_SIZE = 1000;  // if more than this many entries, expire early
+    this.REQUEST_CACHE_MAX_ITEMS = 1000;  // if more than this many entries, expire early
+    this.REQUEST_CACHE_MAX_CHARS = 20000000/2; // or more than this total size
   }
 
   this._cache = {};
+  this._cacheCharSize = 0;
+
   this._interval = undefined;
 
 }
@@ -24,18 +29,29 @@ window.DataCache.prototype.store = function(qk,data,freshTime) {
   // 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];
+  this.remove(qk);
 
   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: JSON.stringify(data) };
+  var dataStr = JSON.stringify(data);
+
+  this._cacheCharSize += dataStr.length;
+  this._cache[qk] = { time: time, expire: expire, dataStr: dataStr };
 }
 
+window.DataCache.prototype.remove = function(qk) {
+  if (qk in this._cache) {
+    this._cacheCharSize -= this._cache[qk].dataStr.length;
+    delete this._cache[qk];
+  }
+}
+
+
 window.DataCache.prototype.get = function(qk) {
-  if (qk in this._cache) return JSON.parse(this._cache[qk].data);
+  if (qk in this._cache) return JSON.parse(this._cache[qk].dataStr);
   else return undefined;
 }
 
@@ -82,9 +98,16 @@ window.DataCache.prototype.runExpire = function() {
     // fixme? our MAX_SIZE test here assumes we're processing the oldest first. this relies
     // on looping over object properties in the order they were added. this is true in most browsers,
     // but is not a requirement of the standards
-    if (cacheSize > this.REQUEST_CACHE_MAX_SIZE || this._cache[qk].time < t) {
+    if (cacheSize > this.REQUEST_CACHE_MAX_ITEMS || this._cacheCharSize > this.REQUEST_CACHE_MAX_CHARS || this._cache[qk].time < t) {
+      this._cacheCharSize -= this._cache[qk].dataStr.length;
       delete this._cache[qk];
       cacheSize--;
     }
   }
 }
+
+
+window.DataCache.prototype.debug = function() {
+//NOTE: ECMAScript strings use 16 bit chars (it's in the standard), so convert for bytes/Kb
+  return 'Cache: '+Object.keys(this._cache).length+' items, '+(this._cacheCharSize*2).toLocaleString()+' bytes ('+Math.ceil(this._cacheCharSize/512).toLocaleString()+'K)';
+}