The Delaware Geological Survey, working with the USGS, has created GIS data that presents an "outline" of the State of Delaware.
The outline is available for download as a zipped collection of files (de_outline.zip) that includes a polygon version of the state outline (dgs_de_outline_a.shp) and a line version (dgs_de_outline_l.shp). The outline is also available on the Delaware DataMIL as part of the Map Lab and as an ArcIMS or WMS map service.
This outline combines the landward state boundary lines with a state shoreline, derived from 2002 statewide orthophotography, to create an outline of the state the way most people picture it when they think of it on a map.
While this outline is not Delaware's complete legal boundary, it does represent the most accurate GIS linework available for Delaware's landward boundary lines. The landward lines were mathematically derived by the USGS to run through the locations of Delaware's Boundary Monuments.
Delaware's complete legal boundary (29 Delaware Code, § 201) is more complex. It runs along the mean low water line (as it existed in 1934) for a portion of the New Jersey Shoreline in the north, tracks the center of the shipping channel for the Delaware River and part of the Delaware Bay, and out into the Atlantic Ocean.