Mason-Dixon Line Map to Sell at Auction in October
The rare cartographic artifact, used in the 1820 Missouri Compromise, is estimated to reach up to $1.2 million.
Updated on Oct. 28, 2026 in Geography
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Brunk Auctions will sell an original hand-drawn map of the Mason-Dixon Line via a livestreamed auction on October 29, 2026. The historic document, which was once used in the 1820 Missouri Compromise, carries an auction estimate of $800,000 to $1.2 million.
Why it matters
This map represents the physical record of the survey conducted in the 1760s to settle border disputes between Maryland and Pennsylvania. Its upcoming sale provides a rare look at a foundational artifact of American cartography.
The chart measures 76 inches in length by 6.5 inches in height and has been preserved using a Japanese rice paper mounting. While this primary chart is for sale, a related section detailing the Delaware-Maryland border is held at Princeton University.
The players
Brunk Auctions
An Asheville-based auction house specializing in fine arts and historic artifacts.
Malcolm S. Forbes
The late publisher of Forbes magazine who acquired the map in 1982.
Benjamin Chew
A historical figure whose family held ownership of the document until 1982.
Princeton University
An Ivy League research institution that curates the remaining section of the map.
The details
The document is a survey map created to resolve land disputes by defining the boundary between Maryland and Pennsylvania. To ensure its stability over time, the chart has been remounted onto a backing of Japanese rice paper, a common archival method that strengthens delicate materials without adding significant thickness. It served as a critical reference during the 1820 Missouri Compromise, illustrating its role as a functional tool in national legislative debates.
Timeline
1760s: Survey of the Mason-Dixon Line conducted.
1820: Map used in the Missouri Compromise.
1982: Malcolm S. Forbes purchased the map.
2002: The map changed hands again.
October 29, 2026: The map goes up for auction.
The Tech Race
This document serves as an anchor for understanding the 1820 Missouri Compromise, providing a tangible reference point for the legislative boundary debates of the era. The upcoming auction continues the trajectory of historical artifacts moving from private collections back into the public or institutional eye.
The auction will be livestreamed on October 29, 2026, allowing remote participants to observe the sale of the document. Collectors and researchers should note that the map's current valuation range of $800,000 to $1.2 million reflects its significance to American territorial history.
The takeaway
The Mason-Dixon map provides a unique view into how spatial data was used to resolve national political crises. Interested parties should track the October 29, 2026 auction results to see if the final bid falls within the expected $800,000 to $1.2 million valuation.
Further reading
Explore the history of regional cartography in the Geography section.
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