My very brief summary of my own work on last month's challenge: I didn't do it. I thought about it. Does that count?
The problem, of course, is that I decided I wanted to have the Topo layer complete before beginning work on Comala. That became an impossibly huge project, as my contour-drawing mania started to encompass the surrounding region.
Anyway, Comala will eventually be mapped, and it will have no motorways.
How did everyone else do?
Luciano's Mapper's Challenge #12 - March, 2017 - Ghosts on the Map
This month's challenge is a more manageable scale. It comes from Thilo.
He suggested "mapping things that aren't there anymore."
This is a common enough aspect of urban geography. This article (Los Angeles Times) is a good introduction to the issue in the context of North American urbanism. In Europe, you can find the outlines of ancient Roman amphitheaters, for example.
Some users have done this already, in OGF. There's joschi81's former railway station converted into a concert hall, in Tarott. I placed a "former railroad right-of-way" when I mapped the area surrounding the Irhoborin Refugee Settlement in Duvar, which can just barely be made out on the map (look for "Rail Street").
So this month's challenge is to map something that isn't there anymore. Use your imagination, think about the history of your territory, and go for it.
Since I'm working on Comala, I think I might place a small, abandoned pre-Colonial city "under" the modern Ardispherian city. I was planning on approaching the city at least semi-historically (not at rigorously as user Pawl has been doing, but a similar concept). So I will draw a plan and place some buildings for the pre-Colonial city in a layer for Comala, which rather than uploading, I'll just keep for reference as I develop the city.