Modularity is a key aspect in software engineering as it comes with several benefits like reusability, extensibility and maintainability. Although it is a well established concept, it has not received much attention when it comes to model-driven software development. Over time, metamodels tend to evolve and grow in complexity to encompass new aspects and features. If modularization steps are not taken and metamodels are extended intrusively, they can become difficult to maintain and to extend. With the increased complexity, the modularization can become even more challenging. In this work, we present a novel approach to assist the modeler in the task of modularization. Our approach addresses the problem from a graphical perspective. The proposed tool support displays a layered structure, where each layer has certain level of abstraction, and allows the modeler to organize metamodels inside the layers. In this layered structure, the metamodels should only depend on metamodels with the same or a higher abstraction level and should not take part in cyclical dependencies. The tool provides the modeler with full control over the modularization process and full knowledge about the relations between the metamodels, thus facilitating the modularization task greatly.