Gathering business requirements
Before we start to figure out how many forests, domains, and domain controllers to create, we need to gather some data to help us make an accurate design that agrees with the core business requirements.
Understanding the organizational structure correctly is vital to designing any access management system. An organizational chart is a good place to start with. It will give you an idea of to whom you need to talk to collect the relevant data that will help your design.
For example, if you need to know what your software development department requires from the directory services, the best person to talk to will be the technical lead or architect of the team. They will be able to give you the exact answer you are looking for. If you ask the same question to the managing director, the answer may not be that accurate. So, before you seek the answers to your questions, you need to find the correct source.