1) I am pretty sure that an area with a high population density has : A. a large area of arable land. It might seem that if there is a lot of people the area should be small, but, actually the richer and the longer area- the more people and land to exploit.
2) I bet, cultural convergence occurs more rapidly with improved transportation. I think that delivering goods is one of the best ways that helps convergence develop and improve.
3) As for me an example of diffusion is : Native American foods were taken to Europe to feed people and livestock. As you can see in this example, some features of one culture transports to another one.
Do hope you will find it helpful!
