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GCN : February 2015
be integrated. According to Usery, the team found that if the resolution of two datasets – say transportation data su- perimposed on image data – was within about 6.4 meters, users would perceive the data as being integrated. But unless both datasets were already geocoded using the same projection sys- tem, getting the two datasets to align correctly can be a major problem. For each data set, an application needs to be created to perform the integration. In the case of integrating transporta- tion data with underlying imagery, said Usery, USGS worked with researchers at the University of Southern California. In similar fashion, USGS provided support to another group to integrate hydrography data with contour layers in the National Map. Of course, integrating data sets col- lected by agencies would be much faster, easier and less expensive, if the data sets were created using standardized meta- data – the data about the data, includ- ing geographic coordinates and object labels. To address the problem, CEGIS is con- sidering a “semantic” approach that al- lows data to be used across application and agency boundaries. “We are primarily looking at ontology and semantics as a way to integrate data across a variety of organizations and dif- ferent kinds of data layers,” said Usery. As it is now, government agencies at all levels – as well as the private sector – ap- ply different labels to features, spatial concepts and other data. Accordingly, CEGIS is working to develop a single integrated language or ontology for de- scribing geospatial data. “We’re taking geospatial data and building an ontology for the data based on all of our features, relationships and interrelationships of features, and then we structure the data using RDF – re- source description framework,” said Usery. “If our data is structured in that form and other data is structured as RDF we can actually bring the data sets together.” In fact, USGS did just that with data it brought in from the Environmental Protection Agency, which was also in RDF format. “We just ran an automatic query to locate all of the EPA pollution sites within five miles a local firehouse,” said Usery. DEALING WITH LEGACY DATA Not surprisingly, the biggest snag to implementing a robust scheme for orga- nizing metadata is the existence of large amounts of legacy data. According to Usery, USGS has not con- verted all of its data to RDF. “Our data resides in GIS format and it works very well,” he said. “There are lots of proce- dures designed around those things and we can’t just completely change over and lose all the legacy developments that we’ve done around GIS platforms.” Instead, the team has developed a tool that allows analysts to take any section of vector data sets and convert it to RDF. For now, Usery said, at USGS most ef- forts to integrate geospatial data contin- ue to be between agencies that share an immediate interest in the specific data. “We try to leverage data from other agencies and not have to collect all the data ourselves,” he said. • GCN FEBRUARY 2015 • GCN.COM 29 When building the National map, the CEGIS team realized that different layers of the map – hydrography, transportation, contours – were compiled separately, making it difficult to make the layers look as though they matched up. NATIONALMAP.GOV 0215gcn_028-029.indd 29 2/4/15 2:00 PM