Difference between a Layer and Tier?

Difference between a Layer and Tier?

Layer:
It refers to the separation of the logic (i.e the code and design) that is developed for an application in different files.

Tier:
It refers to the physical location of the Layer files.

example:
In an ASP.NET web site, we create GUI web forms, business logic , data access
logic, database all in one computer. In this case, we have 4 layers and 1 Tier.
if the GUI Web Forms,business logic, data access logic and database are all in
different computers, we have 4 layers and 4 Tiers.