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Mapping the Congo:
Building and Using a Spatial Database

Early in the development of the Congo Project, existing map resources were found to be inadequate for the kind of biogeographic analyses planned. The project required both broad spatial coverage and detailed information about habitat conditions of potential importance for understanding fish distributions. Existing maps, beyond a map scale of 1:100,000 were generally unavailable. And while the available maps do provide sufficient detail to broadly describe stream channels where surveys were to take place, they did not provide a convenient method for storing and retrieving stream channel data. Digital data were needed and many digital maps would be needed in order to view the basin as a whole. Map information at multiple scales was required. While some existing maps indicate the locations of important channel features, such as major rapids, chutes, and falls, other important habitat features were not delineated. Therefore detailed, spatial descriptions of macrohabitat elements were also needed by the project.

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Geographic information systems data (GIS) have met the need for rapid access to stream data at map scales between 1:100,000 and 1:2M and have offered the capacity to update stream data throughout the Congo basin. Through collaboration with the Freshwater Science Program at World Wildlife Fund, we employ a river and watershed dataset to map stream channels throughout the large study area encompassed by this project. The dataset, called HydroSHEDS, provides the best detail available for river channel locations and their watershed boundaries.

Remote sensing data and analyses provide a birds-eye view of unique habitats and potential sampling sites above and below important channel features. Working over half a century ago, Robert (1946) described three major physiographic sections of the lower Congo. Within each river section, satellite data analyses provide locations and descriptions of macrohabitat elements. The method for obtaining this information consists of three steps. First, computer algorithms subdivide images into "objects," or groups of pixels. Second, the analyst describes the macrohabitat elements s/he would like to identify. Third, and last, an algorithm is developed to extract the image objects that match those descriptions. This simple description encapsulates the essential elements of the object-oriented, contextual classification methods being used to map macrohabitats in the lower Congo River. For an illustration of some of this work, see the AMNH BioBulletins Congo Visualization.

Specimen localities from the field collections that are part of this project have been plotted using GIS and remote sensing data; once identification of species can be confirmed these data will be compared to historic data from ichthyological collections from several museums (eg., American Museum of Natural History, New York, USA; The Africa Museum, Tervuren, Belgium; Musée National d'Histoire Naturelle, Paris, France; Museum of Comparative Zoology, Harvard, USA, The Natural History Museum, London, UK). Maps indicating the fine-scale distribution of individual species within the study area are also being compiled.

Ongoing geospatial and hydrological analyses, tied to specimen and habitat data, will allow us to investigate many evolutionary questions. The peculiarly complex hydraulic and geologic features of the Lower Congo River make this a model system for such studies. Future research is geared at correlating river hydraulic conditions, geologic control and biological conditions to understand distributional patterns and elucidate underlying mechanisms of population linkages and speciation.

© 2007 American Museum of Natural History Back to Ichthyology Department