I've created a city and then encountered a mine not far away. So I just though I would construct the buildings in its direction, so that when I got there I would be able to explore the mine.
When I choose what I want to build, I can see where can I do it, thanks to the green squares. But after placing a building, I was not able to place another further in that direction. I thought I could build in any adjacent square to the city, but sometimes some squares aren't available (but become available later).
So, what's the logic behind this feature?