Store background setting in hash. Fixes #632

js/id/id.js

@@ -92,10 +92,19 @@ window.iD = function () {
         return context;
     };
 
-    context.background()
-        .source(_.find(iD.layers, function(l) {
-            return l.data.name === 'Bing aerial imagery';
-        }));
+    var q = iD.util.stringQs(location.hash.substring(1));
+    if (q.layer) {
+        context.background()
+                .source(_.find(iD.layers, function(l) {
+                    return l.data.sourcetag === q.layer;
+                }));
+    }
+    if (!context.background()) {
+        context.background()
+            .source(_.find(iD.layers, function(l) {
+                return l.data.name === 'Bing aerial imagery';
+            }));
+    }
 
     return d3.rebind(context, dispatch, 'on');
 };

js/id/renderer/background.js

@@ -152,9 +152,22 @@ iD.Background = function() {
         return background;
     };
 
+    function setPermalink(source) {
+        var tag = source.data.sourcetag;
+        var q = iD.util.stringQs(location.hash.substring(1));
+        if (tag) {
+            location.replace('#' + iD.util.qsString(_.assign(q, {
+                layer: tag
+            }), true));
+        } else {
+            location.replace('#' + iD.util.qsString(_.omit(q, 'layer'), true));
+        }
+    }
+
     background.source = function(_) {
         if (!arguments.length) return source;
         source = _;
+        setPermalink(source);
         return background;
     };