map 图表上不同大小的段与 ggplot2 / ggchart

Question

I have the following map chart

library(dplyr)
library(ggmap)    
library(ggplot2)  
register_google(key = "xxx")
map5 <- get_googlemap("Zurich", zoom = 6, scale = 1, style = s)
map5 %>% ggmap


ggmap(map5)
DZ <- c(46.7985, 8.2318)
DE <- c(51.1657, 10.4515)
FR <- c(47.0260, 4.8400)
IT <- c(44.4949,11.3426)
df5 <- data.frame(rbind(DE, FR, IT)) %>% as_tibble
colnames(df5) <- c('latitude', 'longitude') 
df5 <- df5 %>% select(longitude, latitude) %>% mutate(name=c('DE', 'FR', 'IT'), name2 = "DZ", lon2=DZ[2], lat2=DZ[1], route=paste(name, name2, sep='_'))

pmap <- ggmap(map5) +
  geom_point(data = df5, aes(x = longitude, y = latitude, color = route))+
  geom_point(aes(x = DZ[2], y = DZ[1], color = "DZ"))
#geom_line(data = data2, aes(x = lon, y = lat, group = pair))

routecols=c('orange', 'lightblue', 'green')
for (i in 1:nrow(df5)) {
  pmap <- pmap + geom_segment(color = routecols[i],x= df5$longitude[i], y = df5$latitude[i], xend=df5$lon2[i], yend=df5$lat2[i])#,arrow = arrow(length = unit(0.5, "cm")))
}
pmap <- pmap +scale_color_manual(name = "", values = c('IT_DZ'='green', 'FR_DZ'='lightblue', 'DE_DZ'='orange', 'DZ'='pink'))
pmap

QUESTION : How can I take a size into account? I'm looking for something like this, ideally varying sizes along the same line, so that the direction is clear: