为 stat_density2d 图手动设置 scale_alpha

Question

我想专门使用 ggplot2 中的 stat_density2d 绘制当地建设的月度地图。我正在使用以下代码：

library(ggmap)
options(stringsAsFactors=T)

mar_2016 <- structure(list(Latitude = c(47.6064785, 47.6086266, 47.61556306,
                                        47.5335102, 47.53424442, 47.62629031, 47.66231885, 47.55882248,
                                        47.63847192, 47.63847192, 47.63847192, 47.63846822, 47.66045328,
                                        47.64787497, 47.6774562, 47.61126358, 47.61126358, 47.62041964,
                                        47.56586818, 47.56600353), Longitude = c(-122.3313647, -122.32373921,
                                                                                 -122.33276181, -122.3473748, -122.29267751, -122.32268625, -122.28147251,
                                                                                 -122.36343703, -122.36995433, -122.36995433, -122.36995433, -122.36979987,
                                                                                 -122.30463329, -122.37841989, -122.31846715, -122.31515559, -122.31515559,
                                                                                 -122.35567747, -122.3694264, -122.36942834)), .Names = c("Latitude",
                                                                                                                                          "Longitude"), row.names = c(NA, -20L), class = "data.frame")

apr_2016 <- structure(list(Latitude = c(47.62373953, 47.61304116, 47.57543057,
                                        47.59216, 47.66411106, 47.71560842, 47.55499461, 47.55878986,
                                        47.5224678, 47.5224678, 47.63419063, 47.70380892, 47.6309837,
                                        47.60766995, 47.52517771, 47.68700879, 47.68495153, 47.6733502,
                                        47.61578904, 47.66961751, 47.62981265, 47.62126347, 47.60219778,
                                        47.6086266, 47.52835462, 47.67514813, 47.67514813, 47.66513236,
                                        47.56720557, 47.66590858), Longitude = c(-122.30442288, -122.34060091,
                                                                                 -122.39628552, -122.29016643, -122.34337082, -122.31338271, -122.38583914,
                                                                                 -122.26472731, -122.35949442, -122.35949442, -122.35408737, -122.37250127,
                                                                                 -122.3076156, -122.32802388, -122.36489489, -122.38298825, -122.36237138,
                                                                                 -122.35121936, -122.33727143, -122.36591715, -122.29125798, -122.32173169,
                                                                                 -122.33348074, -122.32373921, -122.39195911, -122.28949534, -122.28949534,
                                                                                 -122.28937395, -122.39185006, -122.2962011)), .Names = c("Latitude",
                                                                                                                                          "Longitude"), row.names = c(412L, 416L, 417L, 426L, 427L, 428L,
                                                                                                                                                                      429L, 434L, 437L, 438L, 454L, 456L, 475L, 489L, 490L, 491L, 492L,
                                                                                                                                                                      493L, 494L, 495L, 496L, 507L, 510L, 516L, 525L, 526L, 527L, 528L,
                                                                                                                                                                      529L, 541L), class = "data.frame")


denny_park = get_map(location=c(-122.3437739, 47.6193031), zoom=15)
ggmap(denny_park) +
  geom_density2d(data = apr_2016, aes(x = Longitude, y = Latitude), size = 0.3) +
  stat_density2d(data = apr_2016,
                 aes(x = Longitude, y = Latitude, fill = ..level.., alpha = ..level..), size = 0.01,
                 bins = 16, geom = "polygon") + scale_fill_gradient(low = "green", high = "red") +
  scale_alpha(range = c(0, 0.3), guide = FALSE) +
  ggtitle("April 2016")

ggmap(denny_park) +
  geom_density2d(data = mar_2016, aes(x = Longitude, y = Latitude), size = 0.3) +
  stat_density2d(data = mar_2016,
                 aes(x = Longitude, y = Latitude, fill = ..level.., alpha = ..level..), size = 0.01,
                 bins = 16, geom = "polygon") + scale_fill_gradient(low = "green", high = "red") +
  scale_alpha(range = c(0, 0.3), guide = FALSE) +
  ggtitle("March 2016")

产生 and

如何手动设置 stat_density() 填充参数来为两个图提供相同的图例？根据这个question调用MASS::kde2d计算出..level..参数。手动调用它会给出一个列表：

R> apr_2016_kde <- MASS::kde2d(apr_2016$Longitude, apr_2016$Latitude)
R> str(apr_2016_kde)
List of 3
 $ x: num [1:25] -122 -122 -122 -122 -122 ...
 $ y: num [1:25] 47.5 47.5 47.5 47.5 47.6 ...
 $ z: num [1:25, 1:25] 23.2 27 30.2 32.7 34.2 ...

这 question 非常接近，但抱怨错误：未知参数：在 ggplot2 版本 2.1.0

中中断 stat_density2d()

Answer 1

在两个图中将相同的 limits 参数添加到 scale_fill_gradient。例如，scale_fill_gradient(low = "green", high = "red", limits=c(0,70000))（或您希望的任何范围）。然后相同的颜色将映射到每个图中的相同值。

这是我添加的限制后的图：

(注意：您的问题标题提到 scale_alpha，但您问题的 body 询问如何获得相同的填充图例。我假设您想要相同的填充图例每个情节，但如果你想要不同的东西，请告诉我。）

为 stat_density2d 图手动设置 scale_alpha

Manually setting scale_alpha for stat_density2d plot

r

ggplot2

colors

ggmap

kernel-density