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America’s 95,000 miles of coastline are subject to natural and man-made processes that continually alter its shape and character. The accuracy, consistency, and currency of our national shoreline need to be frequently ensured, especially during this era of rapid coastal development. Countless applications depend on NOAA’s National Spatial Reference System to determine where the land meets the sea, including: ■ producing state-of-the-art nautical charts for safe, efficient, and competitive maritime commerce; ■ defining America’s marine territorial limits; ■ constructing safe buildings, roads, and bridges; and ■ delineating property lines to minimize boundary disputes. NOAA has led the way in developing new applications for GPS. For example, using GPS with aerial photography, we can locate any point on the land below to within about a foot. The remarkable efficiencies made possible by such precise positioning data can be magnified by feeding the data into a Geographic Information System (GIS). A GIS assembles information from a wide variety of sources, including ground surveys, existing maps, and aerial photos. In a GIS, specific information about a place — such as the locations of utility lines, roads, streams, and buildings — is layered over a set of geodetic control. With a computer, regional planners can use the layers individually or in various combinations — for example, to determine how to improve traffic flow, merge construction with existing utility systems, or protect the public from potential natural disasters. And because a GIS stores data digitally, information can be quickly and economically updated, easily reproduced, and made widely available.