Overarching: Scope: What is the scope of this ICS security architecture?
What ICS systems are used for what purposes within the scope of this architecture?
For each type of ICS used in the business and within the scope of this architecture, identify the name of the ICS type, describe its function, and relate its name and function to the business. For example, if there are 30 similar ICS "Paint mixing control" systems that control similar processes (e.g., These systems are used to mix large batches of paint.), they should be listed as a single entry along with the business purpose (e.g., They provide paint that covers all of the particle boards shipped for desks and chairs.). But if each performs a different function with different issues and effects, they should be listed separately. Add rows as needed to meet the need.
The scope of the architecture is up to the enterprise. Generally, it is a good idea to have a scope that covers a class of similar ICS facilities, a business unit, or an enterprise.