How do they work?
There is always an origin country from which money starts to move towards a final country of destination.
It's not always so straightforward though. Money could pass through one or more conduit countries before arriving to the final destination.
Money could also take a round trip, going from the destination to a conduit and back to the destination. This kind of investements are called inversions. A nation could have more than one role: it could be origin, destination and conduit at the same time.
Each flow of money between countries has also a certain degree ofthat depends on how much confidence there is in the estimates.