Shouldn't it just be mileage-based? I mean, you can drive from one end of Russia to the other, and encounter wildly different cultures, but have stayed on the same "continent"
Russia spans 2 continents, so ya couldn't.
I find the distinction between Asia and Europe as separate continents to be laughably stupid. It's obviously one landmass, and any decision about where Europe starts and Asia begins is a purely arbitrary one, as Turkey and Russia demonstrate really well.