It is close, and if you consider Washington as a district there is a meridian exactly 77 degrees west somewhere in there. But I am here eyeballing maps and if the "Washington meridian" is considered the point of the capital it is ~ 1000 feet west of -77.0, should have chosen Stanton park. Seeing as Washington was a planned city I wonder if the capitol point was supposed to be -77.0 west but limitations in surveying accuracy put it where it is. A thousand foot error is not bad for 1800. In fact the very public line at Greenwich is off by ~ 50 feet.

On the subject of eyeballing maps are there any online openstreetmap derivatives that have better cartography tools? (crosshair, lat long at specific point, distance and bearing lines, etc) I probably could install qgis for it, and osmand has a bunch of these tools. but the default osm page sort of sucks here.

Presumably defined rather than just happened, but not surveyed exactly enough. The US Capitol building is at 77.009°W.