r - ggplot map with points: size, colour, legend, aesthetics problems -

i have piece of code:

ggplot(legend = false) +  geom_polygon(data = map.df, size = 0.1, aes(long, lat, group = group, colour = "grey80", fill = ind_vul)) +  scale_fill_gradient2(low = "blue", high = "red", midpoint = mean(map.df$ind_vul, na.rm = true)) +  geom_point(data = puntos.df, aes(as.numeric(long), as.numeric(lat), colour = geografico), size = 2) + facet_wrap(~municipio, scales = "free") +  tema.mapas    

and found several problems (obviously related ignorance of topic), problems following (all related, see ggplot throwing error in weird circumstances):

• the size parameter in geom_polygon working oddly, outside of aes has no effect , inside of ignored, if there no colour parameter.

• the colour parameter ignored (again in geom_polygon) in code above saids colour="grey80" contour line of polygon in colour , "grey80" appears legend of points!

since colour='grey80' , size=0.1 not asking column of map.df should outside of aes call. in other words, when colour inside aes, ggplot thinks you're telling base color of plot on column in data, or if given literal string have here, create mapping between string , entry in usual color palette. mapping aesthetic literal string can useful technique in cases, different setting aesthetic value. outside of aes, color color named "grey80" , use specific color.

[adapted comments , expanded slightly]