Step with me if you will onto the slippery slope of enterprise architecture definition.  I try to capture the boundaries of the enterprise in a single simple layered boxes-and-lines diagram.  Relationships are conveyed through adjacency and separation helps define inappropriate lines of communications.  While the definition is my preferred first deliverable it is based on at least three categories of gathered information and models.

  1. Use Cases are great tools for capturing, analyzing and validating the activities of the architecture.  They provide a simple illustration of the people and systems the enterprise cares about and the service or services it provides to its consumers,

  2. Sequence diagrams of the activities that create and deliver these services, and

  3. Org charts, phone directories, and management hierarchies of the organization the political, fiscal, and physical constraints imposed on it.   

Developed incrementally, using each to validate the others.  Each and every change cascades back onto the other models.   There will be the temptation to leave partial sketches behind and start over.  RESIST !! A few complete, cohesive, balanced visualizations are all you need for the first pass.