Different types of evidence syntheses
The purpose of a systematic review is to provide as objective and accurate response as possible to a specific question, based on all available research on the subject. A systematic review is appropriate when some research studies point in one direction and others point in a different direction. In a systematic review we weigh the results of the studies together and report on what the research as a whole says about the specific question.
The purpose of a systematic map is to provide a comprehensive picture of the literature within a limited area of research. A systematic map is appropriate when the question of interest is broad and the subjects of the studies differ too much. The conclusions of a systematic map relate to the characteristics of the studies. What has been studied, where the studies were conducted, whether any research focus is particularly common or whether there are research gaps, etc. In this way, we can identify areas where it is possible to conduct systematic reviews and areas that would require more research.
Summary of scientific literature
The purpose of a summary of the scientific literature is to provide an overview of the literature within a limited area of research. Such a summary is appropriate when time and resources are lacking to do a systematic map. The literature search is not done with the goal of finding all studies. The conclusions relate mainly to the characteristics of the studies themselves, in other words what has been studied, whether any research focus is particularly common or whether there are research gaps, etc. The conclusions are more preliminary, because not all research studies on the subject are included in a summary of scientific literature.