diff --git a/plugins/portal-level-numbers.user.js b/plugins/portal-level-numbers.user.js
index c5cfa195..9f8fe33c 100644
--- a/plugins/portal-level-numbers.user.js
+++ b/plugins/portal-level-numbers.user.js
@@ -2,7 +2,7 @@
 // @id             iitc-plugin-portal-level-numbers@rongou
 // @name           IITC plugin: Portal Level Numbers
 // @category       Layer
-// @version        0.1.2.@@DATETIMEVERSION@@
+// @version        0.1.3.@@DATETIMEVERSION@@
 // @namespace      https://github.com/jonatkins/ingress-intel-total-conversion
 // @updateURL      @@UPDATEURL@@
 // @downloadURL    @@DOWNLOADURL@@
@@ -19,50 +19,16 @@
 // PLUGIN START ////////////////////////////////////////////////////////
 
 // use own namespace for plugin
-window.plugin.portalLevelNumbers = function() {};
+window.plugin.portalLevelNumbers = function() {
+};
+
+window.plugin.portalLevelNumbers.ICON_SIZE = 12;
+window.plugin.portalLevelNumbers.MOBILE_SCALE = 1.5;
 
 window.plugin.portalLevelNumbers.levelLayers = {};
 window.plugin.portalLevelNumbers.levelLayerGroup = null;
 
-// Use portal add and remove event to control render of portal level numbers
-window.plugin.portalLevelNumbers.portalAdded = function(data) {
-  data.portal.on('add', function() {
-    plugin.portalLevelNumbers.renderLevel(this.options.guid, this.getLatLng());
-  });
-
-  data.portal.on('remove', function() {
-    plugin.portalLevelNumbers.removeLevel(this.options.guid);
-  });
-}
-
-window.plugin.portalLevelNumbers.renderLevel = function(guid,latLng) {
-    plugin.portalLevelNumbers.removeLevel(guid);
-
-    var p = window.portals[guid];
-    var levelNumber = p.options.level;
-    var level = L.marker(latLng, {
-      icon: L.divIcon({
-        className: 'plugin-portal-level-numbers',
-        iconAnchor: [6,7],
-        iconSize: [12,10],
-        html: levelNumber
-        }),
-      guid: guid
-      });
-
-    plugin.portalLevelNumbers.levelLayers[guid] = level;
-    level.addTo(plugin.portalLevelNumbers.levelLayerGroup);
-}
-
-window.plugin.portalLevelNumbers.removeLevel = function(guid) {
-    var previousLayer = plugin.portalLevelNumbers.levelLayers[guid];
-    if(previousLayer) {
-      plugin.portalLevelNumbers.levelLayerGroup.removeLayer(previousLayer);
-      delete plugin.portalLevelNumbers.levelLayers[guid];
-    }
-}
-
-var setup =  function() {
+window.plugin.portalLevelNumbers.setupCSS = function() {
   $("<style>")
     .prop("type", "text/css")
     .html(".plugin-portal-level-numbers {\
@@ -75,12 +41,140 @@ var setup =  function() {
             -webkit-text-size-adjust:none;\
           }")
   .appendTo("head");
+}
+
+window.plugin.portalLevelNumbers.removeLabel = function(guid) {
+  var previousLayer = window.plugin.portalLevelNumbers.levelLayers[guid];
+  if(previousLayer) {
+    window.plugin.portalLevelNumbers.levelLayerGroup.removeLayer(previousLayer);
+    delete plugin.portalLevelNumbers.levelLayers[guid];
+  }
+}
+
+window.plugin.portalLevelNumbers.addLabel = function(guid,latLng) {
+  var previousLayer = window.plugin.portalLevelNumbers.levelLayers[guid];
+  if (!previousLayer) {
+
+    var p = window.portals[guid];
+    var levelNumber = p.options.level;
+    var level = L.marker(latLng, {
+      icon: L.divIcon({
+        className: 'plugin-portal-level-numbers',
+        iconSize: [window.plugin.portalLevelNumbers.ICON_SIZE, window.plugin.portalLevelNumbers.ICON_SIZE],
+        html: levelNumber
+        }),
+      guid: guid
+    });
+    plugin.portalLevelNumbers.levelLayers[guid] = level;
+    level.addTo(plugin.portalLevelNumbers.levelLayerGroup);
+  }
+}
+
+window.plugin.portalLevelNumbers.updatePortalLabels = function() {
+
+  var SQUARE_SIZE = L.Browser.mobile ? (window.plugin.portalLevelNumbers.ICON_SIZE + 3) * window.plugin.portalLevelNumbers.MOBILE_SCALE
+                                     : (window.plugin.portalLevelNumbers.ICON_SIZE + 3);
+
+  // as this is called every time layers are toggled, there's no point in doing it when the layer is off
+  if (!map.hasLayer(window.plugin.portalLevelNumbers.levelLayerGroup)) {
+    return;
+  }
+
+  var portalPoints = {};
+
+  for (var guid in window.portals) {
+    var p = window.portals[guid];
+    if (p._map) {  // only consider portals added to the map
+      var point = map.project(p.getLatLng());
+      portalPoints[guid] = point;
+    }
+  }
+
+  // for efficient testing of intersection, group portals into buckets based on the defined rectangle size
+  var buckets = {};
+  for (var guid in portalPoints) {
+    var point = portalPoints[guid];
+
+    var bucketId = L.point([Math.floor(point.x/(SQUARE_SIZE*2)),Math.floor(point.y/SQUARE_SIZE*2)]);
+    // the guid is added to four buckets. this way, when testing for overlap we don't need to test
+    // all 8 buckets surrounding the one around the particular portal, only the bucket it is in itself
+    var bucketIds = [bucketId, bucketId.add([1,0]), bucketId.add([0,1]), bucketId.add([1,1])];
+    for (var i in bucketIds) {
+      var b = bucketIds[i].toString();
+      if (!buckets[b]) buckets[b] = {};
+      buckets[b][guid] = true;
+    }
+  }
+
+  var coveredPortals = {};
+
+  for (var bucket in buckets) {
+    var bucketGuids = buckets[bucket];
+    for (var guid in bucketGuids) {
+      var point = portalPoints[guid];
+      // the bounds used for testing are twice as wide as the rectangle. this is so that there's no left/right
+      // overlap between two different portals text
+      var southWest = point.subtract([SQUARE_SIZE, SQUARE_SIZE]);
+      var northEast = point.add([SQUARE_SIZE, SQUARE_SIZE]);
+      var largeBounds = L.bounds(southWest, northEast);
+
+      for (var otherGuid in bucketGuids) {
+        // do not check portals already marked as covered
+        if (guid != otherGuid && !coveredPortals[otherGuid]) {
+          var otherPoint = portalPoints[otherGuid];
+
+          if (largeBounds.contains(otherPoint)) {
+            // another portal is within the rectangle - remove if it has not a higher level
+            if (portals[guid].options.level > portals[otherGuid].options.level) continue;
+            else coveredPortals[guid] = true;
+            break;
+          }
+        }
+      }
+    }
+  }
+
+  for (var guid in coveredPortals) {
+    delete portalPoints[guid];
+  }
+
+  // remove any not wanted
+  for (var guid in window.plugin.portalLevelNumbers.levelLayers) {
+    if (!(guid in portalPoints)) {
+      window.plugin.portalLevelNumbers.removeLabel(guid);
+    }
+  }
+
+  // and add those we do
+  for (var guid in portalPoints) {
+    window.plugin.portalLevelNumbers.addLabel(guid, portals[guid].getLatLng());
+  }
+}
+
+// as calculating portal marker visibility can take some time when there's lots of portals shown, we'll do it on
+// a short timer. this way it doesn't get repeated so much
+window.plugin.portalLevelNumbers.delayedUpdatePortalLabels = function(wait) {
+
+  if (window.plugin.portalLevelNumbers.timer === undefined) {
+    window.plugin.portalLevelNumbers.timer = setTimeout ( function() {
+      window.plugin.portalLevelNumbers.timer = undefined;
+      window.plugin.portalLevelNumbers.updatePortalLabels();
+    }, wait*1000);
+
+  }
+}
+
+var setup = function() {
+
+  window.plugin.portalLevelNumbers.setupCSS();
 
   window.plugin.portalLevelNumbers.levelLayerGroup = new L.LayerGroup();
-
   window.addLayerGroup('Portal Levels', window.plugin.portalLevelNumbers.levelLayerGroup, true);
 
-  window.addHook('portalAdded', window.plugin.portalLevelNumbers.portalAdded);
+  window.addHook('requestFinished', function() { setTimeout(function(){window.plugin.portalLevelNumbers.delayedUpdatePortalLabels(3.0);},1); });
+  window.addHook('mapDataRefreshEnd', function() { window.plugin.portalLevelNumbers.delayedUpdatePortalLabels(0.5); });
+  window.map.on('overlayadd overlayremove', function() { setTimeout(function(){window.plugin.portalLevelNumbers.delayedUpdatePortalLabels(1.0);},1); });
+
 }
 
 // PLUGIN END //////////////////////////////////////////////////////////