Others develop theories to explain economic phenomena such as unemployment or inflation. Geographers study the distribution of both physical and cultural phenomena on local, regional, continental, and global scales. Geographers specialize, as a rule. Economic geographers study the regional distribution of resources and economic activities. Political geographers are concerned with the relationship of geography to political phenomena local, national, and international.
Physical geographers study the distribution of climates, vegetation, soil, and land forms.
Urban and transportation geographers study cities and metropolitan areas, while regional geographers study the physical, climatic, economic, political, and cultural characteristics of regions, ranging in size from a congressional district, to a State, country, continent, or the entire world. Medical geographers study health care delivery systems, epidemiology, and the effect of the environment on health. GIS is widely used in weather forecasting, emergency management, resource analysis and management, and other activities. Historians research and analyze the past. They use many sources of information during their research, including government and institutional records, newspapers and other periodicals, photographs, interviews, films, and unpublished manuscripts such as diaries and letters.