Evidence Gap Maps (EGMs) are closely linked to the concept of rigorous impact evaluation (RIE).
EGMs provide a visual representation of systematic reviews (SR) and single scientific studies (often RIEs) available in a certain sector or field, structured around a framework of interventions and outcomes. This means, EGMs are visual compilations of (rigorous) evidence on the impact of policies and programmes in a specific sector or thematic area. This makes it easy for decision-makers to get an overview, of where evidence is already available to be used and where evidence needs to be generated because of evidence gaps.
Here and here you can learn more about EGMs.