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.
A range of different approaches to evidence mapping and synthesis have been developed to support evidence informed policy making. In 2016, (Miake‐Lye, Hempel, Shanman, & Shekelle, 2016) conducted a systematic review of evidence maps in the health sector. The authors identified 145 titles, of these, 34 publications explicitly presented evidence maps and five publications used a mapping methodology without presenting a map. The authors conclude that there is diversity in definition and methods for mapping, so that stakeholders cannot necessarily know what to expect if they commission an evidence map or seek to identify existing maps. In addition, as there is no repository for evidence maps, maps are difficult to locate and authors are less likely to build on existing approaches. One purpose of this paper is to propose some general principles for evidence maps.