atChange - The default. One sign stands at the start of each section and none along it. A
section mostly starts where the value changes, which is where the road posts its own.along - The sign repeats down the stretch at a fixed screen spacing, so a reader zoomed into
the middle of a long one still sees the value in force. A stretch too short on screen to fit a
sign draws none.A stretch can run 50 km. So under atChange, a reader zoomed in past its start sees no sign
until the next change, as on the road itself.
Where a section's signs are posted along the stretch they belong to.