In this study, a method for hierarchical examination and visualization of GSM data using the Self-Organizing Map (SOM) is described. The data is examined in few phases. At first temporally averaged data is used and then, in each phase some of the data is discarded and the rest is examined in more detail. The SOM is used both in clustering and in visualization. The actual clustering is performed to the nodes of the SOM to lower the computational cost and to help to understand better the properties of the clusters.