The USA has some of the biggest cities in the world and more than three-quarters of its people live in cities or towns This means that there are also some very empty places which have not changed much since the first Europeans arrived The government has kept some of them as national parks beautiful natural places where people are not allowed to build houses or factories Many artists have photographed the beautiful parks of America One of the most famous is Ansel Adams who was born in San Francisco a few years before the earthquake of 1906 Two of his favourite places were Yosemite in northern California which has been a park since 1890 and the coast of California