Agriculture & Biology
recreation users
100%
national parks
53%
valleys
51%
psychosocial factors
36%
travel
17%
automobiles
16%
U.S. National Park Service
13%
social problems
11%
ecological value
10%
environmental sustainability
9%
tourism
9%
qualitative analysis
9%
communication (human)
8%
interviews
7%
Earth & Environmental Sciences
national park
50%
valley
38%
transportation system
16%
travel behavior
9%
environmental values
9%
social problem
8%
qualitative analysis
8%
environmental sustainability
7%
twentieth century
7%
freedom
7%
travel
6%
automobile
6%
tourism
6%
communication
5%
services
4%
Chemical Compounds
Qualitative Analysis
61%
Communication
51%
Flexibility
44%
Medicine & Life Sciences
Recreational Parks
86%
Psychology
14%
Crowding
9%
Social Problems
8%
Automobiles
7%
Communication
5%
Interviews
4%
Engineering & Materials Science
Tourism
6%
Automobiles
4%
Sustainable development
4%
Communication
2%