The aim of this paper is to describe the procedure used for the Milan agglomeration Strategic Noise Mapping, as defined by Environmental Noise Directive (2002/49/EC). City of Milan is a complex case study because of the presence of a plurality of sources: road traffic, railway traffic (also tram traffic) and aircraft noise (Linate airport). The assessment method is based on the guidelines contained in the "Good Practice Guide for Strategic Noise Mapping and the Production of Associated Data on Noise Exposure" (WG-AEN). The study of noise generated from several sources was carried out with the integrated use of both numerical models and Geographic Information Systems (GIS). Numerical models allow us to estimate of noise levels in large areas near to a specific noise source and GIS enable the efficient acquisition, management and elaboration of geo-referenced data representative of territory, sources and buildings. By means of the study of specific GIS application it was possible to predict the global noise exposure for overall sources, by overlapping the noise maps of the single noise sources.