Stumbled on a 1954 map where California's coast was drawn 50 miles off

Found this old Shell road map at an estate sale. The whole San Diego coastline is shifted west by about 50 miles. Anyone know if that was a surveying error or just lazy cartography back then?

2 comments

2 Comments

angela_dixon2d ago

Actually, that sounds like a specific surveying error from the U.S. Coast and Geodetic Survey maps of that era. They used base points that were later found to be offset in some regions, especially along the Pacific coast. Check the map's legend for a "datum" note - if it says something like "San Diego base" or "1927 North American Datum," that's the issue. Those old surveys had flaws because they relied on ground measurements that didn't account for the Earth's curvature properly. You can find corrected topo maps from the late 1960s online for comparison. It's not lazy cartography, just the limits of what they could do with the tools back then.

wilson.emma1d ago

Has anyone checked if the problem might actually be from how those old maps were printed, like the paper shrinking or stretching over time? I remember reading that some of those old lithographic processes could warp the paper slightly, throwing off the grid lines by a fraction of an inch (which is a lot when you're scaling up). That could explain the offset without blaming the surveyors at all, since the printing tech back then wasn't exactly precision.