Study area in the greater Chicago, Illinois. General area of mosquito trap locations for 2004 to 2007 (grey shaded areas) and locations of all weather stations with data for the years under analysis are included. Cook county and DuPage county are the area of analysis, while data from the five surrounding counties provided additional support for the spatial interpolation of variables. Mosquito trap locations are shown as gray areas to be illustrative of the general pattern of the traps, rather than to show specific locations, which varied somewhat from year to year. Of the 1263 hexagons (not shown) used for the spatial analysis, 409 (32%) had a trap location in them in at least one of the years.