Here is my stab at it. I think most people are correct in saying that the first 2 numbers are coordinates which take you to Copley Square. The last digit is actually an elevation. The question is in what units?
Well, I believe it is in Cubits. To make sense of it all, 342.242026 Royal Egyptian Cubits is about 587.391732 feet or about 58 stories. What is at an elevation of 58 stories in Copley Square? Well....this:
A mass damper system in the John Hancock Tower
Welcome back dynamic stabilization....