The principal physical feature of the region is the Potomac River, so it is natural that the corresponding feature of the park system is along the river banks. Below Washington, where the broad lakelike scenery exists, parkways are under construction or contemplated on the Virginia side to Mount Vernon and on the Maryland shore to Fort Washington. Above Washington a park is projected to preserve the natural scenery of the Palisades, rapids, woodlands, and Great Falls of the Potomac, together with the Patowmack Canal, built by George Washington, and the Chesapeake & Ohio Canal on the Maryland side of the river. The Commission has taken an active part in the effort to have the public buildings of Washington grouped and arranged not only for the convenience and beauty of the result but also that they may fit into the future plans for streets, highways, and parks, and thus promote the orderly development of the city and region. When the first important step in the public-buildings program was taken in 1926 the Commission urged the purchase of all of the land necessary for a plan of the group as a whole instead of undertaking individual building projects as separate units in the scheme. The problems of parking and transit facilities in relation to the public-buildings groups have caused the Commission great concern, and efforts have been made to secure the cooperation of the architects in charge of the building program in order to solve these problems. In all of its activities concerning the public-buildings program the Commission has been guided by the principles announced by the plan of 1901, under which Federal buildings will be concentrated along the axis of the Mall and about the White House. The Commission has given favorable consideration to an enlargement of this program by which semipublic buildings and possibly State buildings might be located along East Capitol Street in order to help the balance between the northwest and the eastern portions of the city of Washington. In the same way the Commission advises the appropriate authorities on matters of zoning and control of use of private property. Zoning has now been adopted not only in the District but also in the Maryland suburban area and in Arlington County and Fairfax County, Va. Also Alexandria has prepared a zoning plan. It is hoped that in the not distant future other portions of the Maryland and Virginia areas may be added to this list. In matters relating to zoning in the District, the Commission has contributed statistical data and expert opinion, and was particularly active in the segregation of single-family houses from 2-family and community groups.