Hi Bony - the purpose of the number is to identify that specific location along the roadway. Roads are laid out using what they call "stationing" which is simply incremental measurements along the centerline, or possibly the baseline if the layout is offset from the centerline as a rural interstate would be. Station 1 would be 100 feet from station zero. In the example in the video, that number stamp is 108200 feet plus an additional 50 feet from the zero station on that road. That is a simple example - in the real world there are equations at the end of each curve that complicate the simplicity of stationing. A curve is basically an arc that smooths the intersection of two tangent lines. The equations are necessary to adjust for the "shortcut" that the curvature takes in relation to the two tangent lines. This is probably much more than you wanted to know. I tried to stop but I couldn't, ha.

The different increments for different surfaces is a very good question that I can't answer. Some long-dead civil engineer made that decision, and I'm sure it has some logic, but I never could find it, ha.