I've found that the structure that we have in place in my city (Philadelphia) is pretty well organized and efficient for large incidents. I volunteer as a Second Responder (I come in to support First Responders if needed for large scale situations, such as natural disasters or public safety/public health concerns).
I think the most important consideration is ensuring the use of common protocol across all departments/agencies. I've provided an example of how my city approaches the issue of commonality and linked the original city document below. (I really wish we could embed images but imgur is easy enough)