Add documentation on network map vis options.

doc/Extensions/Network-Map.md

@@ -15,3 +15,41 @@ Either remove mac or xdp depending on which you want.
 
 A global map will be drawn from the information in the database, it is worth noting that this could lead to a large network map. 
 Network maps for individual devices are available showing the relationship with other devices.
+
+One can also specicify the parameters to be used for drawing and updateing the network map.  
+Please see http://visjs.org/docs/network/ for details on the configuration parameters.
+```php
+$config['network_map_vis_options'] = '{
+  layout:{
+      randomSeed:2
+  },
+  "edges": {
+    "smooth": {
+        enabled: false
+    },
+    font: {
+        size: 12,
+        color: "red",
+        face: "sans",
+        background: "white",
+        strokeWidth:3,
+        align: "middle",
+        strokeWidth: 2
+    }
+  },
+  "physics": {
+    "forceAtlas2Based": {
+      "gravitationalConstant": -800,
+      "centralGravity": 0.03,
+      "springLength": 50,
+      "springConstant": 0,
+      "damping": 1,
+      "avoidOverlap": 1
+    },
+    "maxVelocity": 50,
+    "minVelocity": 0.01,
+    "solver": "forceAtlas2Based",
+    "timestep": 0.30
+  }
+}';
+```