Data Sources and Structure

Summary

Effective use of GIS data in distributed hydrologic modeling requires understanding of type, structure, and scale of geospatial data used to represent the watershed and runoff processes. GIS data often lacks sufficient detail, space-time resolution, attributes, or differs in some fundamental way from how the model expects the character of the parameter and how the parameter is measured. Existing data sources are often surrogate measures that attempt to represent a particular category with direct or indirect relation to the parameter or physical characteristic. Generation of a surface from measurements taken at points, reclassification of generalized map categories into parameters, and extraction of terrain attributes from digital elevation data are important operations in the preparation of a distributed hydrologic model using GIS. Having transformed the original map into useable parameter maps, the parameter takes on the characteristic data structure of the original map. Thus, the data structure inherent in the original GIS map has lasting influence on the hydrologic process simulated using the derived parameters. In the following chapter we turn to the generation of surfaces from point data.