We propose a model to represent graphically the information system and the impact of cyber events (e.g., attacks, countermeasures) as a prismatic instance of n-sides. The approach considers information about all entities composing an information system (e.g., users, IP addresses, communication protocols, physical and logical resources, etc.), as well as information about the attacker's knowledge, motivation and capabilities. The base of the prism is represented as an n-side polygon (e.g., triangle, square, pentagon, etc.) which depicts the internal information of the system, whereas the height of the prism is represented as a single axis which depicts the external information of the system. We propose geometrical operations to determine the impact of cyber security events (i.e., area, volume, event coverage, residual risk, and potential collateral damages). A case study is proposed at the end of the paper to show the applicability of the model in a scenario with multiple attacks