解决ggplot2中scale_shape_manual导致geom_point填充消失的问题

我正在绘制河流浓度-流量格局与农业、城市用地占比的关系图，示例数据如下：

df.tri<-structure(list(site_no = c("01312000", "01349150", "01349840", 
"01349950", "01356190", "01357500", "013621955", "01362200", 
"0136230002", "01362370", "01362497", "01362500", "01413088", 
"01415460", "01421618", "01422738", "01422747", "0143400680", 
"01434021", "01434025", "01435000", "04213500", "04214500", "04215000", 
"04215500", "04218000", "04218518", "0422026250", "04229500", 
"04230500", "04231000", "04231600", "04232034", "04232050", "0423205010", 
"04232100", "04240180", "04249000", "04250200", "04250750", "04260500", 
"04269000"), Slope = c(0.19, 0.1, -0.01, 0.42, 0.11, 0.19, 0.61, 
0.48, 0.69, 0.69, 0.43, 1.08, -0.14, 0.24, 0.29, 0.26, 0.52, 
0.24, 0.17, 0.28, 0.46, 1.31, 0.87, 0.64, 0.81, 0.26, 0.58, 0.3, 
0.11, 0.37, 0.07, 0.68, 0.24, 0.21, 0.5, 0.1, 0.2, -0.01, 0.06, 
-0.09, 0.27, 0.27), Type = c("Mobilization", "Mobilization", 
"Stationary", "Mobilization", "Stationary", "Mobilization", "Mobilization", 
"Mobilization", "Mobilization", "Mobilization", "Mobilization", 
"Mobilization", "Dilution", "Mobilization", "Mobilization", "Mobilization", 
"Mobilization", "Mobilization", "Mobilization", "Mobilization", 
"Mobilization", "Mobilization", "Mobilization", "Mobilization", 
"Mobilization", "Mobilization", "Mobilization", "Mobilization", 
"Mobilization", "Mobilization", "Mobilization", "Mobilization", 
"Mobilization", "Mobilization", "Mobilization", "Stationary", 
"Stationary", "Stationary", "Stationary", "Stationary", "Mobilization", 
"Mobilization"), DEVNLCD06 = c(0.68, 6.16, 0, 4.72, 55.42, 7.65, 
6.07, 2.18, 0.71, 1.23, 2.16, 2.03, 2.32, 1.54, 1.93, 3.35, 2.97, 
0, 0.08, 0, 0.6, 4.06, 7.15, 5.48, 10.27, 6.75, 17.32, 22.77, 
4.92, 6.51, 8.57, 6.17, 10.47, 63.05, 38.18, 4, 4.48, 8.06, 0.34, 
2.98, 1.34, 1.19), PLANTNLCD06 = c(0.01, 59.75, 0, 5.34, 3.22, 
24.25, 0.23, 0.19, 0.03, 0.07, 1.51, 0.5, 9.48, 19.08, 32.62, 
26.9, 31.24, 0, 0, 0, 0.23, 34.57, 45.19, 46.45, 25.32, 49.94, 
33.19, 33.73, 34.8, 62.4, 64.81, 45.91, 50.93, 18.72, 32.62, 
40.93, 42.55, 39.55, 1.87, 33.51, 11.05, 2.65)), row.names = c(NA, 
-42L), class = "data.frame")

将城市用地占比（DEVNLCD06）设为X轴，农业用地占比（PLANTNLCD06）设为Y轴，通过Type列的不同水平区分点形状，用Slope列的绝对值设置点颜色，初始代码可实现该效果：

ggplot(df.tri, aes(x=DEVNLCD06, y=PLANTNLCD06)) +
  geom_point(aes(shape=as.factor(Type), color=abs(Slope)), size = 4)

但使用scale_shape_manual将Mobilization设为上箭头（形状码2）、Dilution设为下箭头（形状码6）、Stationary设为空心圆（形状码1）后，点的填充效果消失：

ggplot(df.tri, aes(x=DEVNLCD06, y=PLANTNLCD06)) +
  geom_point(aes(shape=as.factor(Type), color=abs(Slope)), size = 4)+
  scale_shape_manual(values = c("Mobilization" = 2, "Dilution" = 6, "Stationary" = 1))

尝试了scale_color_manual、scale_fill_manual等多种scale函数组合均未解决问题，如何在使用scale_shape_manual时保留点的填充效果？

问题核心在于你选择的形状属性：形状2（上箭头）、6（下箭头）、1（空心圆）属于仅支持边框着色的形状，这类形状没有填充区域，无法通过fill参数实现填充效果，只能用color控制边框颜色。

你可以根据需求选择以下两种方案：

方案1：改用带填充属性的形状 #

替换为支持填充的形状码，比如实心上箭头（形状码24）、实心下箭头（形状码25）、实心圆（形状码16），通过fill绑定abs(Slope)实现渐变填充，同时可设置统一边框颜色增强区分度：

ggplot(df.tri, aes(x=DEVNLCD06, y=PLANTNLCD06)) +
  geom_point(aes(shape=as.factor(Type), fill=abs(Slope)), 
             color="black", # 可选：统一边框颜色
             size = 4)+
  scale_shape_manual(values = c("Mobilization" = 24, 
                                "Dilution" = 25, 
                                "Stationary" = 16))+
  scale_fill_viridis_c() # 用渐变颜色映射Slope绝对值

方案2：保留空心形状，强化颜色渐变效果 #

如果坚持使用空心箭头和空心圆，直接用color绑定abs(Slope)实现边框颜色渐变，可通过stroke参数增加边框粗细，让渐变效果更明显：

ggplot(df.tri, aes(x=DEVNLCD06, y=PLANTNLCD06)) +
  geom_point(aes(shape=as.factor(Type), color=abs(Slope)), 
             size = 4,
             stroke=2) # 可选：增加边框粗细
+ scale_shape_manual(values = c("Mobilization" = 2, 
                                "Dilution" = 6, 
                                "Stationary" = 1))+
  scale_color_viridis_c() # 用渐变颜色映射Slope绝对值

内容的提问来源于Stack Exchange，提问作者Ryan