diff --git a/code/map_data_calc_tools.js b/code/map_data_calc_tools.js
index 276e38f0..80bb5e0f 100644
--- a/code/map_data_calc_tools.js
+++ b/code/map_data_calc_tools.js
@@ -10,34 +10,42 @@
 // http://wiki.openstreetmap.org/wiki/Slippy_map_tilenames
 
 
-window.zoomToTilesPerEdge = function(zoom) {
-//  var LEVEL_TO_TILES_PER_EDGE = [65536, 65536, 16384, 16384, 4096, 1536, 1024, 256, 32];
-//  return LEVEL_TO_TILES_PER_EDGE[level];
+window.getMapZoomTileParameters = function(zoom) {
+  // these arrays/constants are based on those in the stock intel site. it's essential we keep them in sync with their code
+  // (it may be worth reading the values from their code rather than using our own copies? it's a case of either
+  //  breaking if they rename their variables if we do, or breaking if they change the values if we don't)
   var ZOOM_TO_TILES_PER_EDGE = [32, 32, 32, 32, 256, 256, 256, 1024, 1024, 1536, 4096, 4096, 16384, 16384, 16384];
-  return ZOOM_TO_TILES_PER_EDGE[zoom] || 65536;
+  var MAX_TILES_PER_EDGE = 65536;
+  var ZOOM_TO_LEVEL = [8, 8, 8, 8, 7, 7, 7, 6, 6, 5, 4, 4, 3, 2, 2, 1, 1];
+
+  return {
+    level: ZOOM_TO_LEVEL[zoom] || 0,  // default to level 0 (all portals) if not in array
+    tilesPerEdge: ZOOM_TO_TILES_PER_EDGE[zoom] || MAX_TILES_PER_EDGE,
+    zoom: zoom  // include the zoom level, for reference
+  };
 }
 
 
-window.lngToTile = function(lng, zoom) {
-  return Math.floor((lng + 180) / 360 * zoomToTilesPerEdge(zoom));
+window.lngToTile = function(lng, params) {
+  return Math.floor((lng + 180) / 360 * params.tilesPerEdge);
 }
 
-window.latToTile = function(lat, zoom) {
+window.latToTile = function(lat, params) {
   return Math.floor((1 - Math.log(Math.tan(lat * Math.PI / 180) +
-    1 / Math.cos(lat * Math.PI / 180)) / Math.PI) / 2 * zoomToTilesPerEdge(zoom));
+    1 / Math.cos(lat * Math.PI / 180)) / Math.PI) / 2 * params.tilesPerEdge);
 }
 
-window.tileToLng = function(x, zoom) {
-  return x / zoomToTilesPerEdge(zoom) * 360 - 180;
+window.tileToLng = function(x, params) {
+  return x / params.tilesPerEdge * 360 - 180;
 }
 
-window.tileToLat = function(y, zoom) {
-  var n = Math.PI - 2 * Math.PI * y / zoomToTilesPerEdge(zoom);
+window.tileToLat = function(y, params) {
+  var n = Math.PI - 2 * Math.PI * y / params.tilesPerEdge;
   return 180 / Math.PI * Math.atan(0.5 * (Math.exp(n) - Math.exp(-n)));
 }
 
-window.pointToTileId = function(zoom, x, y) {
-  return zoom + "_" + x + "_" + y;
+window.pointToTileId = function(params, x, y) {
+  return params.zoom + "_" + x + "_" + y;
 }
 
 
diff --git a/code/map_data_request.js b/code/map_data_request.js
index ecb35e59..56165568 100644
--- a/code/map_data_request.js
+++ b/code/map_data_request.js
@@ -180,8 +180,8 @@ window.MapDataRequest.prototype.refresh = function() {
 
   var bounds = clampLatLngBounds(map.getBounds());
   var zoom = map.getZoom();
-//TODO: fix this: the API now takes zoom (again) rather than portal level, so we need to go back to more like the old API
-  var minPortalLevel = getMinPortalLevelForZoom(zoom);
+
+  var tileParams = getMapZoomTileParameters(zoom);
 
 //DEBUG: resize the bounds so we only retrieve some data
 //bounds = bounds.pad(-0.4);
@@ -189,36 +189,34 @@ window.MapDataRequest.prototype.refresh = function() {
 //var debugrect = L.rectangle(bounds,{color: 'red', fill: false, weight: 4, opacity: 0.8}).addTo(map);
 //setTimeout (function(){ map.removeLayer(debugrect); }, 10*1000);
 
-  var x1 = lngToTile(bounds.getWest(), zoom);
-  var x2 = lngToTile(bounds.getEast(), zoom);
-  var y1 = latToTile(bounds.getNorth(), zoom);
-  var y2 = latToTile(bounds.getSouth(), zoom);
+  var x1 = lngToTile(bounds.getWest(), tileParams);
+  var x2 = lngToTile(bounds.getEast(), tileParams);
+  var y1 = latToTile(bounds.getNorth(), tileParams);
+  var y2 = latToTile(bounds.getSouth(), tileParams);
 
   // calculate the full bounds for the data - including the part of the tiles off the screen edge
   var dataBounds = L.latLngBounds([
-    [tileToLat(y2+1,zoom), tileToLng(x1,zoom)],
-    [tileToLat(y1,zoom), tileToLng(x2+1,zoom)]
+    [tileToLat(y2+1,tileParams), tileToLng(x1,tileParams)],
+    [tileToLat(y1,tileParams), tileToLng(x2+1,tileParams)]
   ]);
 //var debugrect2 = L.rectangle(dataBounds,{color: 'magenta', fill: false, weight: 4, opacity: 0.8}).addTo(map);
 //setTimeout (function(){ map.removeLayer(debugrect2); }, 10*1000);
 
   // store the parameters used for fetching the data. used to prevent unneeded refreshes after move/zoom
-  this.fetchedDataParams = { bounds: dataBounds, mapZoom: map.getZoom(), minPortalLevel: minPortalLevel, zoom: zoom };
+  this.fetchedDataParams = { bounds: dataBounds, mapZoom: map.getZoom(), zoom: zoom };
 
 
-  window.runHooks ('mapDataRefreshStart', {bounds: bounds, zoom: zoom, minPortalLevel: minPortalLevel, tileBounds: dataBounds});
+  window.runHooks ('mapDataRefreshStart', {bounds: bounds, zoom: zoom, minPortalLevel: tileParams.level, tileBounds: dataBounds});
 
   this.render.startRenderPass();
-  this.render.clearPortalsBelowLevel(minPortalLevel);
-
-
+  this.render.clearPortalsBelowLevel(tileParams.level);
   this.render.clearEntitiesOutsideBounds(dataBounds);
 
   this.render.updateEntityVisibility();
 
   this.render.processGameEntities(artifact.getArtifactEntities());
 
-  console.log('requesting data tiles at zoom '+zoom+' (L'+minPortalLevel+'+ portals), map zoom is '+map.getZoom());
+  console.log('requesting data tiles at zoom '+zoom+' (L'+tileParams.level+'+ portals, '+tileParams.tilesPerEdge+' tiles per global edge), map zoom is '+map.getZoom());
 
 
   this.cachedTileCount = 0;
@@ -236,11 +234,11 @@ window.MapDataRequest.prototype.refresh = function() {
   for (var y = y1; y <= y2; y++) {
     // x goes from bottom to top(?)
     for (var x = x1; x <= x2; x++) {
-      var tile_id = pointToTileId(zoom, x, y);
-      var latNorth = tileToLat(y,zoom);
-      var latSouth = tileToLat(y+1,zoom);
-      var lngWest = tileToLng(x,zoom);
-      var lngEast = tileToLng(x+1,zoom);
+      var tile_id = pointToTileId(tileParams, x, y);
+      var latNorth = tileToLat(y,tileParams);
+      var latSouth = tileToLat(y+1,tileParams);
+      var lngWest = tileToLng(x,tileParams);
+      var lngEast = tileToLng(x+1,tileParams);
 
       this.debugTiles.create(tile_id,[[latSouth,lngWest],[latNorth,lngEast]]);
 
diff --git a/code/utils_misc.js b/code/utils_misc.js
index 185cac86..9293dc8c 100644
--- a/code/utils_misc.js
+++ b/code/utils_misc.js
@@ -279,16 +279,10 @@ window.androidPermalink = function() {
 }
 
 
-window.getMinPortalLevelForZoom = function(z) {
-  var ZOOM_TO_LEVEL = [8, 8, 8, 8, 7, 7, 7, 6, 6, 5, 4, 4, 3, 2, 2, 1, 1];
-
-  return ZOOM_TO_LEVEL[z] || 0;
-}
-
 
 window.getMinPortalLevel = function() {
   var z = map.getZoom();
-  return getMinPortalLevelForZoom(z);
+  return getMapZoomTileParameters(z).level;
 }
 
 // returns number of pixels left to scroll down before reaching the