The stakeholder's map (sometimes called Stakeholder Ecology) is a crucial phase in a service design process or any development where you want to focus not only on the user but also on all the people related to your product.
Stakeholders are the people or organizations directly involved or associated with your service. You need to identify who they are and which are the relations between them.
To create a map, you need to research on the industry you are going to deal with, observe the different people implicated, discuss with them. You should identify the more skeptical or enthusiastic ones. Usually, you place your target user in the center, then the directly involved stakeholders around and on the wider circle the associated ones.
Going through a deeper investigation here will enable you to know more about all the people concerned by your solution, the ways they communicate and much more, probably even solutions. Such tool is especially useful when you plan to conduct co-creative sessions.