In the third page (the third paragraph in the right column) of the paper "Time, Clocks, and the Ordering of Events in a Distributed System" by Leslie Lamport, it says that
The reader may find it helpful to visualize a two-dimensional spatial network of processes, which yields a three-dimensional space-time diagram. Processes and messages are still represented by lines, but tick lines become two-dimensional surfaces.
However I failed to visualize them in my head, especially the two-dimensional surfaces. Could anyone make more explanations? An illustrative picture would be excellent.