I don't know if topo maps will show them. I like to do some scouting during the winter to see in the snow high traffic areas. I look for were multiple trails come together. Also, funnels are naturally created by bodies of water, like lakes. I own wet lands that run on one side of a lake. There is a spot in my back woods where 3 trails come into one. This is where I will be placing a tree stand.

Funnels can also be created by gullies or swamps where deer have to travel along a certain path to get through it.

I hope this helps???

T