Within the framework of evidence theory, the construction of mass functions remains an important problem which can considerably influence final results. Several propositions of construction are available in literature but generally, these methods do not consider the belief masses on compound hypotheses and do not exploit all the strengths of the theory. In this article, we propose two methods of grouping hypotheses allowing to reduce the number of focal elements during the construction of mass functions. The first one is based on a well-known approach in cartography and geoinformation fields: Jenks' method. The second one is based on information criteria. We present and confront both methods. Results in a forensic entomology application are then presented.