Much as people can have a preference for cats or dogs, different places also tend to swing one way or the other. And so the populations of the two most popular pets in the world are not spread evenly across the globe. Market research company Euromonitor—a company that studies, among other things, the global market for pet food and pet care—has put together a worldwide picture of cat and dog populations:
Over at the Washington Post, Wonkblog has the numbered breakdown of how many cats and dogs there are in various countries. While the cat vs. dog trends stand out (there are actually more cats than dogs in the U.S.), there's another underlying trend: Americans aren't so much dog or cat people as they are pet people.
In Russia, for example, there are 25 cats and dogs for every 100 people, while the United Kingdom has 28 per 100. The United States, by comparison, has a whopping 46 cats and dogs per 100 people.
Like the U.S., rich western countries do tend to skew more heavily towards cats; according to the Post it's not easy to explain this trend. Part of it may have to do with housing density, as it's easier to keep a cat in an apartment than a dog. Or maybe it's that, while cats serve primarily as companions, dogs can also play a number of useful roles, from guard dog to farm hand to hunting companion.
There are also some interesting historical coincidences. Cats were first domesticated in the Near East, and their popularity there still reigns over dogs. The same is not quite as true for dogs, who were thought to be domesticated in China and Europe.