Gentlemen of the Senate and House of Representatives:
In execution of the powers with which Congress were pleased to invest me by their act entitled "An act for establishing the temporary and permanent seat of Government of the United States," and on mature consideration of the advantages and disadvantages of the several positions within the limits prescribed by the said act, I have by a proclamation bearing date this day (a copy of which is herewith transmitted) directed commissioners, appointed in pursuance of the act, to survey and limit a part of the territory of 10 miles square on both sides of the river Potomac, so as to comprehend Georgetown, in Maryland, and extend to the Eastern Branch.
I have not by this first act given to the said territory the whole extent of which it is susceptible in the direction of the river, because I thought it important that Congress should have an opportunity of considering whether by an amendatory law they would authorize the location of the residue at the lower end of the present, so as to comprehend the Eastern Branch itself and some of the country on its lower side, in the State of Maryland, and the town of Alexandria, in Virginia. If, however, they are of opinion that the Federal territory should be bounded by the water edge of the Eastern Branch, the location of the residue will be to be made at the upper end of what is now directed.
I have thought best to await a survey of the territory before it is decided on what particular spot on the northeastern side of the river the public buildings shall be erected.
George Washington, Special Message Online by Gerhard Peters and John T. Woolley, The American Presidency Project https://www.presidency.ucsb.edu/node/201763