[#vaughn-ddddis], on 2nd chapter:
Problem space is where you define project drivers at a very high level. Think of it as Business Strategy[1]. Solution Space is where we apply Strategic Design around Domain Driven Design (DDD)) and its more closely related business tactics (again [1])
DDD - Bounded Contexts are great tools for the solution space
[1]: Tactic VS Strategy [#vaughn-ddddis]: Vernon, Vaughn. Domain-Driven Design Distilled. Boston: Addison-Wesley, 2016.