Size and Location of Districts. The airport zoning districts shall consist of the following areas for: Baltimore/Washington International Thurgood Marshall Airport—the land area delineated by and contained within a circle, the radius of which is 4 miles from a point with Maryland grid coordinates of E 893,909.99—N 490,279.30; and Martin State Airport—delineated by and contained within a circle, the radius of which is 3.3 miles from a point with Maryland grid coordinates of E 1,478,185.03—N 604,718.69. Boundaries of Districts. Generally. The boundaries of each airport zoning district established by this chapter shall be shown on an airport zoning map filed in the land records of the county where the airport is located. A copy of the map shall be kept at all times in the office of the Administration and shall be open to public inspection during regular business hours. Baltimore/Washington International Thurgood Marshall Airport. A map for Baltimore/Washington International Thurgood Marshall Airport depicting the district established in §A(1) of this regulation shall be filed by the Administration in the land records offices of Anne Arundel County, Baltimore County, and Howard County.