Bibliometric analysis is used as a measuring activity technique for basic research. There are many country level analyses of trends in scientific publications. These analyses give us an understanding of the macro-scale character of scientific activities. However, it is difficult to capture the qualitative evolution of scientific activities through them. In this regard, a meso-scale analysis of science activities, i.e., analysis of "research areas", is suitable for grasping qualitative changes in scientific activities. In this study, we develop a new method for mapping science at the research area level. Our method consists of two parts: constructing research areas from scientific publications and content analysis by experts. Research areas are explored through a co-citation analysis, and a map of science was generated to analyze how research areas relate to each other. This method contributes to endeavours to understand and track the changing nature of science.