library(rgdal)
library(ggplot2)

locs<-read.csv("my_locations.csv")

library(plyr)
#counting duplicates at each location
sp_dups<-data.frame(ddply(locs,.(Longitude,Latitude),nrow))
sp_dups$loc_id<-1:length(sp_dups$Longitude)
sp_dups_df<-merge(sp_dups, locs, by=c("Longitude","Latitude"))

loc<-data.frame(sp_dups_df$Longitude,sp_dups_df$Latitude,sp_dups_df$V1)
loc<-unique(loc)
colnames(loc)<-c("Longitude", "Latitude", "V1")

coordinates(loc)<-c("Longitude","Latitude")
proj4string(loc) <- CRS("+proj=longlat")

loc_df<-data.frame(loc)

theme_opts <- list(theme(panel.grid.minor = element_blank(),
                         panel.grid.major = element_blank(),
                         panel.background = element_blank(),
                         plot.background = element_rect(fill="white"),
                         panel.border = element_blank(),
                         axis.line = element_blank(),
                         axis.text.x = element_blank(),
                         axis.text.y = element_blank(),
                         axis.ticks = element_blank(),
                         axis.title.x = element_blank(),
                         axis.title.y = element_blank(),
                         plot.title = element_text(size=22)))

library(maps)
library(mapdata)

ggplot(data=loc_df, aes(Longitude, Latitude, group=NULL,fill=NULL,size=V1))+#, fill=hole)) + 
  borders(fill="light grey",colour="light grey")+
  geom_point(color="black",alpha=I(7/10))+
  scale_size(range=c(1,7), guide = "legend",labs(size="No. of Populations"))+
  coord_equal()+
  theme_opts