creating Gmap view showing route (line) between two points

Hi,
I'd like to create a Gmap view which would show a route (line) between two points.

In simple way, the idea is:
1) user creates node which has two fields. Both are node references (cities) which have set location (latitude, longitude)
2) Lets say he chose New York and Boston and saved the node.
3) As a result I would like to have a map showing a line linking Boston and New York.

Any idea how to start this?

I already have many cities with locations saved as node type - city.

Now I'd like to let users to create those city pairs and have a view showing them on map as two points linked with a line.

I would really appreciate any hints.