This work characterizes the environment of Culex pipiens sl. in Portugal, using a 7-year data set collected all over the territory from May to October each year. Culex pipiens sl. are the most abundant mosquito complex in Portugal mainland and of medical importance, as they act as vectors for more than 20 species of virus. The abundance data of mosquitoes’ females is used with environmental factors in a geographic information system (GIS) to characterize its habitat, using land use/land cover data, distance to cartographed water bodies, altitude, and latitude. The distribution of mosquitoes by each factor shows mosquito preferences and identifies thresholds between areas of higher/lower abundance for i) altitude in intervals of 100 m, ii) degree of latitude and iii) distance to water in intervals of 1000 m; in the case of land use/land cover, the subset of the most populated classes is identified and aggregated. These thresholds allow the segmentation of the corresponding maps, and the area in common for all the environmental factors considered identifies the area where the risk of disease transmission is significant. To categorize the risk in this broad area and focus mitigation countermeasures, we use the quantity of captures above average from all the data set to identify three categories of increased risk, which allow for a more targeted use of countermeasures and a detailed mitigation planning. This methodology can be used for any other vectors of medical importance, whenever abundance data is available, contributing to reduce costs and human labor and saving the environment from extensive application of toxic products.