A map becomes personal when it includes the place you met someone.

Places acquire private layers that no official map records. A junction is a junction to everyone else and, to you, the spot where a particular conversation happened, and after that you cannot walk through it neutrally again. Everyone is carrying a version of the same city marked up differently. This is why two people can give different accounts of the same street and both be accurate.

Notice your own marked places, since they are easy to walk past without registering. Tell someone about one of them, or take a person you love to the corner where something began. Shared marks are how a map gets passed on.