GUI2 Added selection of background maps

Change-Id: I88ee69fe2ff24bb1b4b3fe633b04f2f1778f3a82
diff --git a/web/gui2/src/main/webapp/app/view/topology/layer/forcesvg/models/force-directed-graph.ts b/web/gui2/src/main/webapp/app/view/topology/layer/forcesvg/models/force-directed-graph.ts
index b511886..24dd029 100644
--- a/web/gui2/src/main/webapp/app/view/topology/layer/forcesvg/models/force-directed-graph.ts
+++ b/web/gui2/src/main/webapp/app/view/topology/layer/forcesvg/models/force-directed-graph.ts
@@ -52,6 +52,10 @@
     height: number;
 }
 
+/**
+ * The inspiration for this approach comes from
+ * https://medium.com/netscape/visualizing-data-with-angular-and-d3-209dde784aeb
+ */
 export class ForceDirectedGraph {
     public ticker: EventEmitter<d3.Simulation<Node, Link>> = new EventEmitter();
     public simulation: d3.Simulation<any, any>;