The City of Tokyo (and Japan in general) is known for so many vending machines.

1.  The City of Tokyo (and Japan in general) is known for so many vending machines. Explain why Tokyo (and Japan) has so many vending machines compared to other retail mechanism, such as corner convenience store or newsstand. How does this phenomenon is related to with a very high population density in Tokyo (and Japan).

2.  In determining the demand curve, we hold "other things constant." Explain what we mean by that, and why the assumption is important in the law of demand.