
Quoting
bigtrees
He should not do anything at the moment. The appointment is on Monday and there is nothing legal that the neighbor can do this weekend that can't be undone later.
I would strongly encourage some additional property research today. It will save the attorney time (saving the OP money) and might resolve the issue more easily.
In particular, I am very confused why the GIS line showing the property boundary was in a widely inaccurate location. GIS lines aren't drawing by kindergarteners with etch-a-sketches. They're drawn by experts who are skilled at reading deeds, surveys, and the like, and the computing systems used show the lines to highly accurate dimensions.
While they aren't legal per se, the lines should be pretty darn accurate. When I've compared the lines to aerial photographs, they were always accurate to within a reasonable degree of accuracy (less than 5' and often about 1' to 2'). So if a line is 50' away from where a person thinks it should be, there is more to story that we don't know.