I’m not an expert. But my understanding is that Topo just doesn’t have the codes and so forth for the unit to use to autoroute. Navigator is set up for autorouting. It is not very good for showing trails, streams, or even small lakes. It has no Topo lines. That’s why I run both. I can switch to Navigator to autoroute in cities that I don’t know very well and then switch over to Topo when hiking or in parks (especially when you want to know which side of the water the cache is located).
It may not be worth it to you to purchase Navigator because other than having more up-to-date roads (Topo is really behind the times) and allowing autorouting Navigator is much worse once you are out of the truck.
