Dengue transmission risk according to DPT. Dengue transmission risk maps as isolines for the annual days of possible transmission (DPT). Left, isolines for the period 1991–2001 (D1). Right, isolines for the period 2001–2011 (D2). Only the isolines of extreme years are shown. When the maximum or minimum differs by zone, both isolines are shown. Each year spans from July of the previous year to June of the indicated year (e.g. 2000 includes 365 days from 1 July 1999 to 30 June 2000).