Do state plane coordinates always begin as longitude and latitude?
In other words, they are not another system that can be calculated without Long. and Lat., correct?
I guess I'm saying, back in 1930+ they came up with the State Plane system. To make that work, however, they had to start with L&L. Today, I am guessing I can simply compare it to a database. But if for example, I have a GPS device and I want to know the Plane Coordinate, I have to convert it.