Evidence maps are a relatively new approach to systematically identify and report the range of research activity in broad topic areas or policy domains. Although they go under various names, they have the common feature of adopting a systematic approach to mapping begins with a broad question, theme or issue which defines the scope of the evidence map. For reasons discussed below, we adopt the term Evidence and Gap Map to refer to the specific approach being proposed for Campbell, and evidence map to refer collectively to the range of approaches which have been adopted. As we describe in Part 2, evidence mapping of various forms has been around for at least 15 years.