An internal product roadmap communicates the effort and activities required to get your product ready for the market. This internal artifact is especially useful to coordiante across your engineering, marketing, sales, and support teams.
A public product roadmap communciates the timeline when you will deliver the features to your customers. Architects and other stakeholders will use this information to plan their implementations and buying decisions. A public roadmap is extrememly valuable and impacts the success of your products in the market. Customers and partners will align their roadmaps to your public product roadmap allowing them to plan accordingly and avoid technical debt.
A program roadmap communicates the planned releases for all the products in the program. If you are not working in a product aligned team, then it will show the planned delivery of projects your team is focused on delivering. Program roadmaps are useful for executive stakeholder and advisory board communication to align teams across the company.
A program roadmap is a high level, strategic artifact, therefore, it should communicate where investments are being made and how you are directing your team's efforts to achieve a goal that is aligned to the overall corporate objectives. Communication of your program roadmap is an opportunity to gain sponsorship, collaboration, and alignment from cross-displinary teams.
Whether you're building a program or product roadmap, the goal is to explain the future and required actions required to achieve your overarching objectives.
Focus first on sequencing the items in your roadmap and then prioritize based on dependencies and impact.