Considering the Culex population, we computed the number of individuals of the initial population, estimat- ing the number of adults that emerge from the larvae laid down in sumps (which we supposed to be the main reservoirs of mosquitoes in urban and sub-urban areas). To this end, we developed a Visual Basic application in order to query the geo-referenced databases in Geomedia and to compute the total length of roads for each municipality of interest. We then computed the number of sumps in each municipality by using the total length of roads (Table 4 ). We assumed that there is an average of one sump for each 30 linear meters of road. This average distance conforms to the standards used by the Ministère des transports du Québec (MTQ) when they install sumps. However, the user of the WNV-MAGS system can modify this value, since it can vary in relation to the considered regions such as urban and rural areas. We also assumed that there are only 20% of sumps containing larvae. This default value can also be modified by the user as well as the average number of Culex adults which emerge from a sump at the beginning of a simulation. These numbers were obtained by consulting data provided by the SOPFIM Company [34] in relation to the monitoring of larval and adult Culex in certain Quebec regions during the summer of 2005.