3.2.1. Trends between noise and greenInitially, a graphic representation of the variations betweennoise and green (trees + field) was produced so as to identifypossible common trends among the six cities. According to Fig. 6three different trends in terms of noise and green can be recognised.
The first one refers to cities like Helsinki and Prague where thereis a parallel decreasing tendency both in the number of noise pix-els and green for each noise band. Moreover, both cities representcases with a very high proportion of quiet areas, which belong in the55 dB(A) band and the highest proportion of green in the same fre-quency. A variation of this trend can also be identified in the citiesof Amsterdam and Rotterdam, where the decreasing tendency innoise and green starts from 60 dB(A) instead of 55 dB(A).
The second trend refers to cities like Brussels, where noise has amore normal distribution among noise bands compared to the firsttrend. Moreover, green and noise follow opposite tendencies in themiddle noise bands demonstrating that the relationship betweenthese two indices is not always proportional.