I've had trouble increasing the radius of the circle on a map. I've tried the scale_size_continuous with maximum size up to 1000, but the circle size remained the same after all. 
My code is in the following:
states <- map_data("state")
gg1 <- ggplot(data=states) +
  geom_polygon(data=states, aes(x=long,y=lat,group=group), 
               fill = "orange", color = "white") + 
  coord_fixed(ratio = 1.3)+
  geom_circle(data = origCity, aes(x0 = Long, y0 = Lat, r = Percent), 
              fill = "black", color = "black", alpha = 0.5, show.legend = FALSE) +
  scale_size_continuous(range = c(20, 5))+
  theme(panel.grid.major = element_blank(),
        panel.grid.minor = element_blank(), 
        panel.background = element_blank())+
  theme(axis.ticks.x = element_blank(),
        axis.title.x = element_blank(),
        axis.text.x = element_blank())+
  theme(axis.ticks.y = element_blank(),
        axis.title.y = element_blank(),
        axis.text.y = element_blank())
print(gg1)
Any suggestions are greatly appreciated!
 
    