When you map some variable to alpha=
inside the aes()
then by default alpha values range from 0.1 to 1 (0.1 for lowest maped variable values and 1 for highest values). You can change it with scale_alpha_continuous()
and setting different maximal and minimal range values.
ggplot() +
geom_polygon(data=all_states, aes(x=long, y=lat, group=group),
color="white", fill="grey80") +
stat_density2d(data=df, aes(x=long, y=lat, fill=..level.., alpha=..level..),
size=2, bins=5, geom='polygon') +
geom_point(data=df, aes(x=long, y=lat),
color="coral1", position=position_jitter(w=0.4,h=0.4), alpha=0.8) +
theme_bw()+
scale_alpha_continuous(range=c(0.1,0.5))