How is the average temperature of a country calculated?

Question

I've seen a few countries with their average temperatures, but I've always wondered how it was calculated.

I mean, you should know that different parts (cities) of a country have different temperatures. So, how is the overall temperature of that country calculated?

Answer 1

You add up all average temperatures for each city and divide that number by the number of cities.

Answer 2

With a rectal thermometer.

Answer 3

add, divide