CPA-I: Inform the broad community of an interesting and useful event, architecture, framework, or concept. CPA-I documents will generally describe implemented, working systems (policies, technical solutions, etc.) rather than abstract concepts or plans. However a CPA-I may also be used to describe broader frameworks or architectures or pilot projects and implementations that did not result in working systems (but provide useful experience regarding approaches that proved not to be viable).
CPA-PR: The purpose of a CPA-PR is to describe technologies or solutions that are proposed as a preferred approach or solution to a particular urban objective, challenge, or service. A CPA-PR is intended to document a particular approach or solution with broad consensus and move it into a period of implementation where operational experience can be gathered and documented. Whereas a CPA-PR document will describe viable approaches or solutions to a specific topic area, a CPA-R will document an approach or solution that has shown viability and success in practice across a variety of cities in terms of culture, scale, climate, etc. As such, a CPA-R must first be published as a CPA-PR. Then, after multiple (at least two independent) implementations have completed and a CPA-I published, the CPA-PR may be considered for advancement to a CPA-R.
CPA-R: The purpose of a CPA-R is to describe technologies or solutions that are uniquely viable, are widely used in cities, and are considered to be the preferred approach or solution to a particular urban objective, challenge, or service. A CPA-R is intended to document a particular approach or solution with broad consensus and considerable successful operational experience. As such, a CPA-R must first be published as a CPA-PR, after which there is a process by which it may progress to the CPA-R stage.