ggplot2如何在地图边界（例如美国州）内保持抖动位置？

Question

有没有办法让地图上的点在地图边界内抖动？在下面的例子中，康涅狄格州西南部的抖动位置最终位于水中或相邻的状态，有没有办法让R抖动位置点但不在地图边界上？

另外，还有其他一些技巧，比如在每个城市附近创建一个表格以列出公司名称？

# 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) 

更改每个经度或纬度一点点，因为在这个问题上，将无法工作，因为有太多的分，我希望的算法解决方案，因为我有很多情况下，这种拥挤和过境可能会出现。 https://stackoverflow.com/questions/22943110/jitter-coordinates

谢谢你的任何建议或答案。

Answer 1

你可以使你自己的jitter函数抖动数据。然后使用SDMTools中的功能pnt.in.poly来检查点是否在多边形内。否则，您只需再次抖动原始点。请参阅下面的例子：

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)