Population density is the number of people in an area, while distribution is about where they are. Generally, the greater the number of people in an area, the greater the potential for disaster. therefore, an earthquake in Alaska will have less impact than one which hits a more densely populated area such as San Francisco. The Pacific Ring of Fire covers a 40,000km horseshoe shape has around 905 of the world's earthquakes and 452 volcanoes. Hundreds of millions of people live in this zone, including over 20 million people close to Popocatépetl volcano in Mexico.