Click here for a full-size version of this week’s map.

This map is a choropleth of the countries of the world. (Do you need a refresher on what a choropleth is? Visit our “Basics” page for a quick primer.) On this map, each country is shaded in accordance with a particular statistic. Countries with a darker shade have higher values for the statistic in question. We did not have reliable data for the countries in grey. Your job is to figure out what statistic is represented by this choropleth.

Stumped? Check back Tuesday, Wednesday, Thursday, and Friday for hints about where to focus your investigation. The answer will be posted on Monday, August 14. Good luck!

Tuesday’s hint: One interesting feature of this map is that Turkey is so dark. The reason why has to do with Turkey’s peculiar tax system.

Wednesday’s hint: Another interesting feature of this map is that the U.S. is the lightest country with a highly developed economy. It is dramatically lighter than Canada, Australia, New Zealand, Japan, and every country in Western Europe. That should be an indication that you’re looking for something in which American government policy differs markedly from the policies of other developed economies.

Thursday’s hint: This is a map in which the light colored countries will probably tell you more than the dark countries. Let’s make a list of some countries that are quite light: Ecuador, Algeria, Nigeria, Turkmenistan, Saudi Arabia, Qatar, the United Arab Emirates, Kuwait, Bahrain. All of these countries have something in common economically. Can you figure out what it is?

Friday’s hint: In 2015, the biggest market for Tesla cars was the United States. Second place was Norway, a country of only 5 million people. Norway has since been passed on Tesla’s list by both China and the United Kingdom, but Tesla still does a brisk business in Norway. Not coincidentally, Norway is the darkest country on this week’s map. What explains that relationship?

Answer: Click here to see an explanation of the answer to this week’s map question.

Next map: Click here to try out our newest map question.