Planet Earth contains some extraordinarily diverse environments, some of which are easily habitable and some not so much. In different areas of Earth, one might find sweltering deserts, dense tropical rainforests, or bone-chilling tundras. Each biome and habitat comes with its own selection of flora and fauna, and it may include physical features such as canyons, volcanoes, rivers, or caves. Human beings have built homes in many different environments, settling the area and organizing it into units such as cities, states, regions, and countries, each with its own points of interest. Shifting trends in human migration have resulted in a human geography that is profoundly different from that of centuries ago.