Use commas to set apart geographical names and to separate items in dates, except for between the month and the day.
When I heard zombies had been located in New York, New York, I knew it was time to move to Los Angeles, California.
It is a good thing that letter made it to 4 Privet Drive, Little Whinging, Surrey, England.
I know the Mayan calendar indicates the end of the world on December 21, 2012, but I am going to stick with Nostradamus because he gave us until 3797.