Banneker was appointed by Secretary of State Thomas Jefferson to serve as an assistant to Andrew Ellicott, who was tasked with surveying the boundaries of the new federal capital, Washington, D.C.

Banneker's role involved using his astronomical knowledge to determine the precise location of boundary markers. He made astronomical observations and performed complex calculations to ensure the accuracy of the survey, thus playing a key role in city planning.

When Pierre Charles L'Enfant, the architect of Washington, D.C., abruptly left the project with the original plans, Banneker's remarkable memory and reconstruction of the city layout proved invaluable in preserving L'Enfant's vision. He was able to recreate the plans almost entirely from memory.

His involvement in the District of Columbia survey further solidified Banneker's reputation as a skilled mathematician and astronomer, demonstrating his abilities on a national scale. His work helped disprove common racist assumptions that existed during this time.