Left: diameter, age, and position of the H ii regions of the HRDS survey in the Galaxy. The dashed green lines show the limit of the survey, the thick black curves are the position of the spiral arms of our Galaxy based on Russeil (2003). The ages are estimated using the grid of 1D simulations at a fixed density at 1 pc (3400 cm^-3) for the initial profile. The galactic electron temperature gradient is taken into account using Eq. (8). Right: age distribution of our sample, the ionizing flux of the regions is indicated by the colour scale.