17  

You could use the fact that internally, a map object returned by the map() function can be recalculated and used again in the map() function. I'd create a list with individual polygons, check which ones have very different longitude values, and rearrange those ones. I gave an example of this approach in the function below*, which allows something like :

您可以使用內部事實，map（）函數返回的地圖對象可以重新計算並在map（）函數中再次使用。我將創建一個包含單個多邊形的列表，檢查哪些具有非常不同的經度值，並重新排列這些多邊形。我在下面的函數*中給出了這種方法的一個例子，它允許類似於：

plot.map("world", center=180, col="white",bg="gray",
   fill=TRUE,ylim=c(-60,90),mar=c(0,0,0,0))

to get

要得到

If I were you, I'd shift everything a bit more, like in :

如果我是你，我會更多地改變一切，比如：

plot.map("world", center=200, col="white",bg="gray",
   fill=TRUE,ylim=c(-60,90),mar=c(0,0,0,0))

The function :

功能 ：

plot.map<- function(database,center,...){
    Obj <- map(database,...,plot=F)
    coord <- cbind(Obj[[1]],Obj[[2]])

    # split up the coordinates
    id <- rle(!is.na(coord[,1]))
    id <- matrix(c(1,cumsum(id$lengths)),ncol=2,byrow=T)
    polygons <- apply(id,1,function(i){coord[i[1]:i[2],]})

    # split up polygons that differ too much
    polygons <- lapply(polygons,function(x){
        x[,1] <- x[,1] + center
        x[,1] <- ifelse(x[,1]>180,x[,1]-360,x[,1])
        if(sum(diff(x[,1])>300,na.rm=T) >0){
          id <- x[,1] < 0
          x <- rbind(x[id,],c(NA,NA),x[!id,])
       }
       x
    })
    # reconstruct the object
    polygons <- do.call(rbind,polygons)
    Obj[[1]] <- polygons[,1]
    Obj[[2]] <- polygons[,2]

    map(Obj,...)
}

*Note that this function only takes positive center values. It's easily adapted to allow for center values in both directions, but I didn't bother anymore as that's trivial.

*請注意，此功能僅采用正中心值。它很容易適應兩個方向的中心值，但我不再煩惱，因為這是微不足道的。

2  

A bit late, but you can also create a shifted map by using a projection (requires the mapproj package):

有點晚了，但你也可以使用投影創建一個移位的地圖（需要mapproj包）：

  map("world", projection="rectangular", parameter=0, 
      orientation=c(90,0,180), wrap=TRUE, fill=T, resolution=0,col=0)

This will shift by 180 degrees. But the difference with 'world2' is that the longitude co-ordinate will be different ([-pi,pi]). All projections of this package put 0 at the centre. And in that case, the 'wrap' option detects the jump correctly.

這將移動180度。但與'world2'的區別在於經度坐標會有所不同（[-pi，pi]）。該套餐的所有預測均以0為中心。在這種情況下，'wrap'選項可以正確檢測跳轉。

'resolution=0' helps to get cleaner borders.

'resolution = 0'有助於獲得更清晰的邊界。

You can easily change the centre longitude by changing the '180' value in the projection description.

您可以通過更改投影描述中的“180”值輕松更改中心經度。

1  

install the latest version of maps (3.2.0).

安裝最新版本的地圖（3.2.0）。

do this:

做這個：

d$lon2 <- ifelse(d$lon < -25, d$lon + 360, d$lon) # where d is your df
mapWorld <- map_data('world', wrap=c(-25,335), ylim=c(-55,75))

ggplot() +
geom_polygon(data = mapWorld, aes(x=long, y = lat, group = group)) +
geom_point(data = d, aes(x = lon2, y = lat))