Section 23.60.010 of the Land Use Code establishes the Shoreline District of the City of Seattle as follows:

There is established the Shoreline District which shall include all shorelines of the City, the boundaries of which are illustrated on the Official Land Use Map, Chapter 23.32. In the event that any of the boundaries on the Official Land Use Map conflict with the criteria of WAC 173-22-040 as amended, the criteria shall control.

All properties located within the Shoreline District shall be subject to both the requirements of the applicable zone classification and to the requirements imposed by this Chapter except as provided in Section 23.60.014.

The Seattle Shoreline Master Program (SSMP) Section 23.60.936 defines "shorelines" as follows:

All the water areas of the City and their associated shorelands together with the lands underlying them: except (A) shorelines of statewide significance; (B) shorelines on segments of streams upstream of a point where the mean annual flow is twenty cubic feet per second or less and the wetlands associated with such upstream segments; and (C) shorelines on lakes less than twenty acres in size and wetlands associated with such small lakes.

The SSMP Section 23.60.944 defines "wetlands" as follows:

"Wetlands" means those areas that are inundated or saturated by surface water or ground water at a frequency and duration sufficient to support, and that under normal circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil conditions. Wetlands generally include swamps, marshes, bogs, and similar areas. Wetlands do not include those artificial wetlands intentionally created from nonwetland sites, including, but not limited to, irrigation and drainage ditches, grass-lined swales, canals, detention facilities, wastewater treatment facilities, farm ponds, and landscape amenities, or those wetlands created after July 1, 1990, that were unintentionally created as a result of the construction of a road, street, or highway. Wetlands may include those artificial wetlands intentionally created form nonwetland areas to mitigate the conversion of wetlands. (The method for delineating wetlands shall follow the most current version of the "Washington State Wetlands Identification and Delineation Manual" as adopted by the State Department of Ecology.)

Field measurement of the location of the 200-foot Shoreline District boundary line may be required or used for the purpose of determining whether a development is located within the Shoreline District. If the relationship of the development to the Shoreline District boundary is unclear on the Official Map, or if the development appears to be bisected by the boundary line, the Director may require the applicant to submit a survey prepared by an engineer or surveyor licensed by the State of Washington. Similarly, if the applicant submits a survey to verify the Shoreline District boundary, the Director shall accept the field verification, provided that the survey is prepared by an engineer or surveyor licensed by the State of Washington.

The boundary line of the Shoreline District was drawn without actual field verification. In addition, the scale of the Official Map is such that it is difficult to determine with precision where the boundary line falls. Because of the potential for error on the Official Map, field measurements can often be a more accurate method of determining where the 200-foot line is actually located.