如何使用gganimate包在R中绘制动态地图？

Question

据我所知，gganimate版本是1.0.3，我们可以使用transition_*函数来绘制动态图。但是当我运行以下代码时，出现错误：

Error in `$<-.data.frame`(`*tmp*`, "group", value = "") : 
  replacement has 1 row, data has 0

代码：

library(ggmap)
library(gganimate)
world <- map_data("world")
world <- world[world$region!="Antarctica",]
data <- data.frame(state = c("Alabama","Alaska","Alberta","Alberta","Arizona"),
                   lon = c(-86.55,-149.52,-114.05,-113.25,-112.05),
                   lat = c(33.30,61.13,51.05,53.34,33.30)
                   )
ggplot()+
  geom_map(data = world,
           map = world,
           aes(long,lat,map_id = region),
           color = '#333300',
           fill = '#663300') +
  geom_point(data = data,
             aes(x = lon, y = lat),
             size = 2.5) +
  geom_jitter(width = 0.1) +
  transition_states(states = state)

Answer 1

您在顶级ggplot()行中没有定义任何数据，因此state中的transition_*毫无用处。

我也不清楚为什么您的代码中具有geom_jitter级。像transition_*一样，它没有要继承的顶级数据/美学映射，因此如果transition_*没有首先触发错误，它也将引发错误。此外，即使我们添加了映射，在给定数据中纬度/经度坐标的范围的情况下，抖动0.1也几乎不会带来视觉上的影响。

您可以尝试以下操作：

# put data in top level ggplot()
ggplot(data,
       aes(x = lon, y = lat))+
  geom_map(data = world,
           map = world,
           aes(long,lat,map_id = region),
           color = '#333300', fill = '#663300',
           # lighter background for better visibility
           alpha = 0.5) + 
  geom_point(size = 2.5) +
  # limit coordinates to relevant range
  coord_quickmap(x = c(-180, -50), y = c(25, 85)) +
  transition_states(states = state)