用ggplot绘制pH值

Question

我正在尝试使用具有纬度，长度，pH值的数据集生成海洋pH值的空间图，如下所示：

head(sample)
  Station       lat     long       pH
1     B17 -23.49174 152.0718 8.222411
2     B23 -23.49179 152.0718 8.199310
3     B26 -23.49182 152.0717 8.140428
4     B28 -23.49183 152.0717 8.100752
5     B30 -23.49185 152.0717 8.068141
6     B31 -23.49187 152.0717 8.048852
7     B32 -23.49187 152.0717 8.043878
8     B33 -23.49188 152.0717 8.052589
9     B34 -23.49189 152.0717 8.085398
10    B35 -23.49191 152.0717 8.092179
11    B36 -23.49191 152.0717 8.103831
12    B38 -23.49194 152.0717 8.195493
13    B40 -23.49194 152.0717 8.289563
14    B43 -23.49197 152.0717 8.305461
15    B49 -23.49202 152.0717 8.319335
16    F17 -23.49180 152.0720 8.019838
17    F29 -23.49194 152.0719 7.827754
18    F31 -23.49194 152.0719 7.906839
19  F31.5 -23.49195 152.0720 7.935676
20  F32.5 -23.49196 152.0720 7.120869
21    F33 -23.49197 152.0720 7.282649
22  F33.5 -23.49198 152.0720 7.209787
23    F34 -23.49198 152.0720 7.185605
24  F34.5 -23.49199 152.0719 7.237628
25    F37 -23.49200 152.0719 7.657356
26    F49 -23.49206 152.0719 8.223883
27    M17 -23.49178 152.0719 8.161814
28    M25 -23.49185 152.0718 7.981371
29    M29 -23.49187 152.0718 7.882754
30    M31 -23.49188 152.0718 7.904225
31    M32 -23.49188 152.0718 7.940181
32    M33 -23.49188 152.0718 8.050878
33    M34 -23.49190 152.0718 8.129610
34    M35 -23.49191 152.0718 8.168780
35    M37 -23.49193 152.0718 8.182910
36    M41 -23.49197 152.0718 8.208416
37    M49 -23.49204 152.0718 8.197651

我正在使用ggplot并且可以生成一个绘制各个位置的图形，但我无法弄清楚为什么它不在位置之间进行插值以显示渐变。我尝试了geom_raster(interpolate=TRUE)和geom_tile，但两者都没有在点之间进行插值。这是因为积分过于稀疏吗？或者我错过了什么？谢谢！

setwd("~/OTI/OTI 2016/R")
library(maps)
library(ggplot2)
library(RColorBrewer)  # for brewer.pal(...)

sample<-read.csv(file="Station locations 2016.csv", header=TRUE, sep=",", strip.white=T)

ggplot(data = sample, aes(x = long, y = lat, fill = pH)) + 
  geom_raster(interpolate = TRUE) +  
  scale_fill_gradientn(colours = rev(rainbow(7)), na.value = NA) +
  theme_bw() +
  coord_fixed() +
  geom_point(colour = "red")

Answer 1

尝试stat_density2d(geom="raster", aes(fill = ..density..), contour = FALSE)