To conduct these tests, we will construct integrated data sets that include key information about the human communities, ecological processes, and physical functions of the metropolitan area. In addition, new mathematical models will be constructed to apply the theory to the functioning of metropolitan Baltimore as an ecological system. The integration begins with the watershed approach, which is fundamental to both ecology and hydrology. Watersheds can be divided into patches that have different ecological and physical structures. Flow path, flow rate, and the distribution of soil saturation level depend on the topography and the characteristics and arrangement of patch types.
Integration requires dividing watersheds into a hierarchy of smaller basins.
The second hierarchy relevant to watershed function is the social-political hierarchy used in planning. While these patches in a social hierarchy differentiate one community from another based upon a certain set of social characteristics, and are the target of different scales of political and social decision making, they also contain mosaics of land cover types that have specific hydrological and ecological functions. The surface cover or land cover hierarchy can therefore be termed an ecological hierarchy, because of the functional contribution of vegetation, soil and inert surfaces to land cover classes. Therefore, land cover patches are common to both the watershed and social hierarchies. The multiple hierarchical nature of watersheds prompts three questions.