Distribution Maps of Fishes in California

Moyle and Mr. Randall used a comprehensive fish database that consisted of about 10 separate fish databases from various agencies recording the presence and absence of a species. These databases varied from one another in structure and were queried separately for each species.

Range maps were produced in accordance with the TNC's method of identifying species presence using three confidence ratings: confident, probable and possible. Information that came from existing databases (both digital and published reports) was categorized as confident. The fish distribution data were graphically displayed on paper maps which were then used to create larger polygons showing species distributions at either the “probable” or “possible” levels of confidence.

These polygons were initially drawn on paper maps (roughly 11 in. x 17 in.) which included locations of fish occurrences from all digital databases possessed, and GIS layers for hydrology (1:500,000 scale) and the state boundary (1:100,000 scale) . The boundaries of the fish range polygons were drawn on paper by Professor Peter Moyle and then digitized on the computer screen by Paul Randall using ARC/INFO GIS software.

The resultant polygons are estimated to be accurate at a scale of roughly 1:1,000,000. This provided adequate resolution for the Hexagon Project which used a small geographic scale grid to compile species lists. A vast majority of the fish polygons were overlaid using the California 1:24,000 scale USGS quadrangle map grid lines to produce fish biodiversity (species richness) maps.