R ggmap 以经度 180 度为中心

Question

我正在使用 R ang ggmap 绘制位于经度 180 度左右的点（参见下面的示例）。 地图大部分是空的。有没有办法将地图以经度 = 180 为中心并将范围限制在点所在的位置？ 换句话说，我有兴趣将 x 轴上的范围限制为 180±14 度。

library("ggmap")
x <- structure(list(Bias = structure(c(5L, 4L, 3L, 3L, 4L, 6L, 6L, 
                                       3L, 3L, 4L, 3L, 5L, 2L, 3L,
                                       3L, 4L, 4L, 4L, 4L, 4L, 4L,
                                       6L, 5L, 4L, 3L, 6L, 5L, 4L,
                                       5L, 4L, 4L, 3L, 6L, 4L, 6L,
                                       4L, 5L, 4L, 4L, 4L, 3L, 3L,
                                       4L, 2L, 4L, 3L, 3L, 6L, 4L,
                                       5L),
                                     .Label = c("(-Inf,-5]",
                                                "(-5,-2]",
                                                "(-2,0]",
                                                "(0,2]",
                                                "(2,5]",
                                                "(5, Inf]"),
                                     class = "factor"), 
                    lat = c(-1.35, -13.24, -14.31, -16.13, -17.15,
                            -17.35, -17.75, -18.05, -18.23, -20.67,
                            -29.24, -34.43, -35.13, -35.9, -37.01,
                            -37.56, -37.67, -38.66, -38.74, -39.01,
                            -39.45, -39.47, -40.32, -40.54, -40.9,
                            -40.9, -41.3, -41.33, -41.73, -41.74,
                            -42.42, -42.71, -43.49, -44.3, -45.02,
                            -45.22, -45.93, -46.16, -46.41, -47.28,
                            -50.49, -52.55, -43.86, -18.15, -12.5,
                            -19.05, -52.55, -44.53, -38.17, -17.23),
                    lon = c(176, -176.19, -178.12, -179.98, 176.9,
                            178.22, 177.45, 178.57, -178.8, -178.72,
                            -177.93, 172.68, 174.02, 175.12, 174.81,
                            178.31, 176.2, 177.99, 176.08, 174.18,
                            175.66, 176.86, 175.61, 173, 174.99,
                            176.21, 173.22, 174.81, 174.28, 171.58,
                            173.7, 170.98, 172.53, 171.22, 168.74,
                            166.88, 170.2, 166.61, 168.32, 167.46,
                            166.3, 169.15, 169.01, 177.42, 177.05,
                            178.17, 169.13, 169.89, 174.7, -178.95)),
               .Names = c("Bias", "lat", "lon"),
               class = "data.frame",
               row.names = c(NA, -50L))
# Map extent
xy <- c(left = min(x$lon), bottom = min(x$lat),
        right = max(x$lon), top = max(x$lat))
# Download the base map
gg <- get_stamenmap(xy, zoom = 5, maptype = "toner-lite")
ggmap(gg) +
  geom_point(data = x, aes(x = lon, y = lat, col = Bias),
             size = 1, alpha = 0.9) +
  scale_color_viridis(discrete = T)

Answer 1

stamen 和数据结构的问题比其他任何问题都大。谷歌地图和一些数据争吵都不是问题。

代码：

# Using your data as basis
x[x$lon < 0, ]$lon <- 2*180 + x[x$lon < 0, ]$lon

# Get map with lon center opposite the Meridian
g <- ggmap(get_googlemap(c(180, 0), zoom = 1), extent = "panel")

# Plot map with boundaries
g + scale_x_continuous(limits = c(0, 360), expand = c(0,0)) +
    scale_y_continuous(limits = c(-70, 70), expand = c(0,0)) + 
    # Plot data points
    geom_point(data = x, aes(x = lon, y = lat, color = Bias),
               size = 1, alpha = 0.9) +
    # Add custom color scheme
    scale_color_viridis(discrete = T)

说明：

如果您将 zoom = 1 与当前的 Google Maps API 一起使用，它会为您提供一点左右经度重叠，您可以根据自己的喜好进行裁剪。

> g$data
        lon       lat
1 -44.64844 -87.75631
2 405.35156 -87.75631
3 -44.64844  87.72862
4 405.35156  87.72862

如果您检查上面原始地图的边界，您会发现我们总共可以使用 450 度经度 (44.64844 + 405.35156)。因此，我们可以将地图缩减为lon = c(0, 360) 和lat = c(-70, 70)（分别使用scale_x_continuous 和scale_y_continuous），这将使中心点正好位于lon = 180 和lat = 0。

但是，您的数据使用正确的经度值 0:-180 (West) 和 0:180 (East)。因此，我们还需要将低于零的经度值更新为 0:360 系统中的对应值。这是通过180 + 180 + lon 实现的（所以longitude = -172 将变成longitude = 188 用于绘图）。

可视化：

Answer 2

无法弄清楚如何使用 ggmap 执行此操作。 但是，这里是使用 ggplot 和 maps 包的解决方案（此处代码的修改版本：World map with ggmap）。

library(maps)
library(ggplot2)

# x is the data.frame defined in the question

# Recenter points
center <- 180
# shift coordinates to recenter x
x$long.recenter <- ifelse(x$lon < center - 180 , x$lon + 360, x$lon)

# shift coordinates to recenter worldmap
worldmap <- map_data ("world", wrap = c(0, 360))

# Plot worldmap using data from worldmap.cp
ggplot(aes(x = long, y = lat), data = worldmap) + 
  geom_polygon(aes(group = group), fill="#f9f9f9", colour = "grey65") + 
  scale_y_continuous(limits = c(-60, 0)) +
  scale_x_continuous(limits = c(180 - 20, 180 + 15),
                     breaks = seq(160, 190, 10),
                     labels = c(160, 170, "180/-180", -170)) +
  coord_equal() +  theme_bw() +
  geom_point(data = x,
             aes(x = long.recenter, y = lat, col = Bias),
             pch = 19, size = 3, alpha = .4) +
  xlab("Longitude") + ylab("Latitude")