A Roadmap is a pre-determined set of states that any particular System (or set of systems) is planned to be in at certain points in time.
Typically it starts with the current state, goes through a series of transitional states, and ends up at a final ideal state.
Of course, time moves on and things change, so when this Roadmap is viewed some time later, the goals may have changed and the ideal end state and indeed some of the transitional states may be altered. But this is fine. Provided baselines are kept, and these changes are managed, the changes on changes can continue happening. The roadmap will always show the latest set of required transitions.