如何用png（）保存它中的ggplot大小？

Question

Map size with lat/long 38.31536111,-76.55011111 is different from map with lat/long 59.5624775,-139.7410994 (plotting points on the map)

while saving it with png()

How to keep the same size? height and width isn't enough?

EDIT: full code

library(maps)
library(ggplot2)
data <- read.csv("data.csv", header=TRUE)
lat = data$lat
long = data$long
world<-map_data('usa')
sf<-data.frame(long=long,lat=lat)
p <- ggplot(height=600, width=800) +
geom_polygon( data=world, aes(x=long, y=lat,group=group)) 
p <- p + geom_point(data=sf,aes(long,lat),colour="white",size=1)
p

data file:

"lat","long"
59.5624775,-139.7410994
42.38748056,-94.61803333

If I remove the first line in the data file, the map size is different (bigger), than when both lines are present

Answer 1

Your code is a bit of a mess mate, so I fixed it into reproducable format below. Solution is already given by @joran - you need to specify size in png() .

library(maps)
library(ggplot2)
#specify size here
png("world.png",height=600,width=800)

#here is a way to create very simple data frame from you coordinates
data <- read.table(textConnection("
lat long 
59.5624775 -139.7410994 
42.38748056 -94.61803333"),header=TRUE,as.is=TRUE)
long=data$long
lat=data$lat
world <- map_data('usa')
sf<-data.frame(long=long,lat=lat)
ggplot() +
geom_polygon(data=world, aes(x=long, y=lat,group=group)) + 
geom_point(data=sf,aes(long,lat),colour="white",size=1)

#this saves png in your current directory
dev.off()

EDIT: Ups, now I made some error in the previous code, now it's fixed.