Who was the American mathematician and astronomer that helped to survey Washington DC and is noted for his correspondence with Jefferson regarding the morality of slaving?

The American mathematician and astronomer you are referring to is Thomas Jefferson's contemporary, Benjamin Banneker. Banneker was instrumental in the surveying of Washington, D.C., and he is well-known for his correspondence with Jefferson, where he challenged the moral implications of slavery and advocated for the rights of African Americans. His efforts significantly contributed to discussions about race and equality in early American history.