I observe systematic errors of longitude differing by about 2 seconds (corresponding to about 200 feet) from positions measured on USGS topo maps in California, New Mexico and Puerto Rico. These errors are always in the same direction, pertain only to the longitude, and so cannot reasonably be attributed to "inaccuracy" which would exhibit randomness in both size and direction.

The GE west longitude is always a larger number than the USGS west longitude describing the same feature on the surface of the earth.

Does anyone know if these differences arise from referencing a different zero longitude, or for some other reason, or what ?