If imagery becomes invalid, remove it from imagery_used

(closes #4827)

modules/core/history.js

@@ -32,10 +32,10 @@ import {
 
 
 export function coreHistory(context) {
-    var imageryUsed = ['Bing'];
     var dispatch = d3_dispatch('change', 'undone', 'redone');
     var lock = utilSessionMutex('lock');
     var duration = 150;
+    var _imageryUsed = [];
     var _checkpoints = {};
     var _stack;
     var _index;
@@ -62,7 +62,7 @@ export function coreHistory(context) {
         return {
             graph: graph,
             annotation: annotation,
-            imageryUsed: imageryUsed
+            imageryUsed: _imageryUsed
         };
     }
 
@@ -294,7 +294,7 @@ export function coreHistory(context) {
 
         imageryUsed: function(sources) {
             if (sources) {
-                imageryUsed = sources;
+                _imageryUsed = sources;
                 return history;
             } else {
                 var arr = _map(_stack.slice(1, _index + 1), 'imageryUsed');

modules/renderer/background.js

@@ -19,6 +19,7 @@ export function rendererBackground(context) {
     var dispatch = d3_dispatch('change');
     var detected = utilDetect();
     var baseLayer = rendererTileLayer(context).projection(context.projection);
+    var _isValid = true;
     var _overlayLayers = [];
     var _backgroundSources = [];
     var _brightness = 1;
@@ -38,6 +39,17 @@ export function rendererBackground(context) {
             }
         }
 
+        // Is the imagery valid here? - #4827
+        var sources = background.sources(context.map().extent());
+        var wasValid = _isValid;
+        _isValid = !!sources
+            .filter(function(d) { return d === baseLayer.source(); }).length;
+
+        if (wasValid !== _isValid) {      // change in valid status
+            background.updateImagery();
+        }
+
+
         var baseFilter = '';
         if (detected.cssfilters) {
             if (_brightness !== 1) {
@@ -123,9 +135,9 @@ export function rendererBackground(context) {
 
 
     background.updateImagery = function() {
-        if (context.inIntro()) return;
+        var b = baseLayer.source();
+        if (context.inIntro() || !b) return;
 
-        var b = background.baseLayerSource();
         var o = _overlayLayers
             .filter(function (d) { return !d.source().isLocatorOverlay() && !d.source().isHidden(); })
             .map(function (d) { return d.source().id; })
@@ -167,7 +179,7 @@ export function rendererBackground(context) {
         var imageryUsed = [];
 
         var current = b.imageryUsed();
-        if (current) {
+        if (current && _isValid) {
             imageryUsed.push(current);
         }