r - ggplot2如何在 map 边界(例如美国州)内保持抖动的位置？

Question

有没有一种方法可以将在 map 上抖动的点保持在该 map 的边界内？在下面的示例中，康涅狄格州西南部的抖动位置最终落入水中或处于邻接状态，是否有办法使位置点抖动R但不在 map 边界上？

或者，是否还有其他技术，例如在每个城市附近创建一个表格组以列出公司名称？

# create a data frame called "ct" of geolocations in two cities near the border of a US state (Connecticut).  Each firm has the same lat and longitude of one of the two cities

> dput(ct)
structure(list(city = structure(c(1L, 1L, 1L, 1L, 1L, 2L, 2L, 
2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 
2L, 2L, 2L, 2L), .Label = c("Greenwich", "Stamford"), class = "factor"), 
    firm = structure(c(1L, 12L, 21L, 22L, 23L, 24L, 25L, 26L, 
    27L, 2L, 3L, 4L, 5L, 6L, 7L, 8L, 9L, 10L, 11L, 13L, 14L, 
    15L, 16L, 17L, 18L, 19L, 20L), .Label = c("A1", "A10", "A11", 
    "A12", "A13", "A14", "A15", "A16", "A17", "A18", "A19", "A2", 
    "A20", "A21", "A22", "A23", "A24", "A25", "A26", "A27", "A3", 
    "A4", "A5", "A6", "A7", "A8", "A9"), class = "factor"), long = c(-73.63, 
    -73.63, -73.63, -73.63, -73.63, -73.55, -73.55, -73.55, -73.55, 
    -73.55, -73.55, -73.55, -73.55, -73.55, -73.55, -73.55, -73.55, 
    -73.55, -73.55, -73.55, -73.55, -73.55, -73.55, -73.55, -73.55, 
    -73.55, -73.55), lat = c(41.06, 41.06, 41.06, 41.06, 41.06, 
    41.09, 41.09, 41.09, 41.09, 41.09, 41.09, 41.09, 41.09, 41.09, 
    41.09, 41.09, 41.09, 41.09, 41.09, 41.09, 41.09, 41.09, 41.09, 
    41.09, 41.09, 41.09, 41.09)), .Names = c("city", "firm", 
"long", "lat"), row.names = c(NA, -27L), class = "data.frame")


library(ggplot2)
# load the map of the United States
all_states <- map_data("state")
# choose to map the borders only of the state of Connecticut
st.map <- subset(all_states, region == "connecticut")

# plot the points for the firms with minimal jitter that still distinguishes each point
ggplot(ct, aes(long, lat)) + 
  geom_polygon(data=st.map, aes(x=long, y=lat, group = group), colour="grey70", fill="white") +
  coord_map() + 
  geom_point(position=position_jitter(width=.1, height=.1), size=2)

像这个问题一样，更改每个经度或纬度的点不会起作用，因为存在太多的点，并且我希望找到一种算法解决方案，因为在很多情况下，可能会出现这种拥挤和跨越边界的情况。 https://stackoverflow.com/questions/22943110/jitter-coordinates

感谢您的任何建议或答案。

Answer 1

您可以创建自己的jitter函数来抖动数据。然后使用pnt.in.poly中的SDMTools函数检查点是否在多边形内。否则，您将再次抖动原始点。参见以下示例:

require(SDMTools)
bounded_jitter <- function(mapping, data, bounds, width, height, ...){
  # data2 is the jittered data
  data2 <- data
  data2[, paste(mapping$x)] <- rnorm(nrow(data), data[, paste(mapping$x)], width/1.96)
  data2[, paste(mapping$y)] <- rnorm(nrow(data), data[, paste(mapping$y)], height/1.96)
  # is it inside the polygon?
  idx <- as.logical(pnt.in.poly(pnts = data2[, c(paste(mapping$x), paste(mapping$y))],  
                                poly.pnts = bounds)[, 'pip'])
  while(!all(idx)) { # redo for points outside polygon
    data2[!idx, paste(mapping$x)] <- rnorm(sum(!idx), data[!idx, paste(mapping$x)], width/1.96)
    data2[!idx, paste(mapping$y)] <- rnorm(sum(!idx), data[!idx, paste(mapping$y)], height/1.96)
    idx <- as.logical(pnt.in.poly(pnts = data2[, c(paste(mapping$x), paste(mapping$y))],  
                                  poly.pnts = bounds)[, 'pip'])
  }
  # the point
  geom_point(data = data2, mapping, ...)
}
# plot the points for the firms with minimal jitter that still distinguishes each point
ggplot(ct, aes(long, lat)) + 
  geom_polygon(data=st.map, aes(x=long, y=lat, group = group), colour="grey70", fill="white") +
  coord_map() + 
  geom_point(size=2) + 
  bounded_jitter(mapping = aes(x=long, y=lat), 
                 data = ct, 
                 bounds = st.map[, c('long', 'lat')], 
                 width = .1, 
                 height = .1)