Walking in forests, hiking, is considered to be necessary for healt in many countries. In United States national parks cover 1.8% of total forest area. In addition, 25% of the forests are so called national forests, which have paths, campsites, wells, beaches, cottages etc. for hikers. In Finland, 20% of the population lives in towns and cities. Also in Finland the people living in cities and towns would need areas that resemble national forests of United states for recreation.
The PDF includes a summary in German.