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AN EXTENDED NATIONAL SPATIAL DATA INFRASTRUCTURE FRAMEWORK: 64 THE ROLE OF OTHER ORGANIZATIONS DEFINITION OF A CITY OR COUNTY EXTENDED FRAMEWORK The starting point for any city or county extended Framework is FGDCâs Framework. Therefore, a county Framework should include geodetic control, orthophoto imagery, elevation, transportation, hydrography, governmental units, and cadastral information. The geodetic control may be supplemented at the local level by local surveys, and the orthophoto imagery could also be supplemented by larger scale coverage than that collected federally. Information on the utility location is important at the local level, and is likely to become more important as the utility industry and public-sector utility services exploit new technologies that require more accurate geospatial data. More detailed elevation data may also be part of the local jurisdictionâs contribution to an LSDI. For example, we already have counties that have 0.5-foot contours derived from orthoimagery produced by the private sector under contract. For the transportation layer at the county level, it is expected that transportation features such as roads will be defined by their edges, and maybe by the spaces corresponding to the road right-of-way in addition to the road centerlines. For hydrography, additional information such as the location of each bank of the watercourse, its navigability for small craft, intakes from rivers and streams, and inputs into the same, may be monitored. For these federal Framework themes it is clear that local level data will enrich most of the layers of the NSDI. A major difference between the local Framework and national Framework is the definition of the content for both the governmental units layer, which accurately depicts a wide range of administrative unit boundaries, and the cadastral information layer, which depicts the legal boundaries of parcels of property ownership. Whereas the cadastral information overlay from the federal NSDI could be expected to include both the Public Lands Survey System (PLSS) used in the western states and federally-owned lands managed by the Bureau of Land Management, the Park Service, and other federal agencies, the local Framework would include details of privately-owned parcels. This is an entirely different magnitude of data
AN EXTENDED NATIONAL SPATIAL DATA INFRASTRUCTURE FRAMEWORK: 65 THE ROLE OF OTHER ORGANIZATIONS collection compared with the supplemental information described in the preceding paragraph. Similarly, whereas the NSDI contains international and state boundaries, the preponderance of other boundary information would be provided to the federal level by state and local levels. Municipal boundaries, voting districts, city wards, county or municipal parks, school attendance areas, and similar administrative boundaries should be provided by the local level. In some cases, the responsibility to collect, integrate, and maintain the data theme lies with the state but has been delegated to the local level. Examples abound of existing files that contain such digital information. Geospatial information describing ownership boundaries and structure footprints is often accompanied by owner name, street address, assessed valuation, and many more attributes (some databases include and make available as public domain data, square footage of buildings, floor plans, number of bathrooms, etc.). A second difference is the reference system, although hopefully this difference will be temporal in nature. Even though it is highly recommended that NAD 83 (North American Datum, 1983), NAVD 88 (North American Vertical Datum, 1988), and latitude and longitude be used as the basis of a positional system in the NSDI, at the local government level this may not be practical. For example, most local surveys are conducted in the State Plane Coordinate system (SPC). Therefore, it may be preferable to use SPC rather than latitude and longitude for some implementations at the local level. The fact that transformation equations exist between the different SPC zones and latitude and longitude lessens the practical impact of this difference. It may eventually mean that the data are available in latitude and longitude but that a separate file in SPC is kept for local daily use. Recent developments in GIS technology allow differences in projection and datum to be overcome âon the fly.â Another major change at the state and local levels would be the inclusion of additional themes. For example, an additional theme at the local level could be the location of public services: schools, hospitals, police and fire stations, etc. Each of these features may be annotated with attributes at a level that could not be done by a national agency, yet the information would be valuable at any level. It is assumed here that the positional and attribute resolution of the data layers at the county level will be the highest (or at least no less than
