Does location affect the color of a tan - i.e. if you tan in Los Angeles does the color of your skin differ if you had tanned in Miami?

No. Location will not affect the color of your tan. But, as a general rule, the further away from the equator you are, the less UV rays there are, so your tan may take a little longer to develop.

Your tan will be affected by how much time you spend in the sun, and your natural skin color.