合并单独几何图层的图例

我正在地图上绘制来自两个单独图层的点数据，并希望在一个图例中显示两个图层的信息。

下面是一些代码来说明问题：

set.seed(42)  
lat1 <- rnorm(10, 54, 12)
long1 <- rnorm(10, 44, 12)
val1 <- rnorm(10, 10, 3)
lat2 <- rnorm(10, 54, 12)
long2 <- rnorm(10, 44, 12)
val2 <- rnorm(10, 10, 3)

df1 <- as.data.frame(cbind(long1, lat1, val1))
df2 <- as.data.frame(cbind(long2, lat2, val2))

library(ggplot2)
library(scales)

f <- ggplot() +
     geom_point(data=df1, aes(x=lat1, y=long1, size=val1, fill=val1), shape=21, alpha=0.6) +
     scale_size_continuous(range = c(2, 12), breaks=pretty_breaks(4)) +
     scale_fill_distiller(direction = -1, palette="RdYlBu", breaks=pretty_breaks(4)) +     
     guides(fill = guide_legend(), size = guide_legend()) +
     theme_minimal()
p <- f + geom_point(data=df2, aes(x=lat2, y=long2, color="val2"), shape=17, size=3) +
     scale_color_manual(values="black",name="")
p

我能做到的最好的办法就是创建两个单独的图例，然后删除其中一个图例标题。理想情况下，实心圆圈和黑色菱形都属于同一个图例的一部分，例如“价值”和黑色菱形将读作例如“不适用”。任何帮助深表感谢！

我们必须绘制两个不同的图例，但将它们移动到彼此靠近（使用负值legend.spacing.y需要 ggplot2_3.0.0）。这种方法产生了另一个问题 - 两个图例没有对齐，因此我们必须绘制另一组钻石（更大以匹配非钻石，但不可见）alpha = 0)

ggplot() +
    geom_point(data = df1, 
               aes(lat1, long1, size = val1, fill = val1), 
               shape = 21, alpha = 0.6) +
    geom_point(data = df2, 
               aes(lat2, long2, color = "val2"), 
               shape = 17, size = 3) +
    geom_point(data = df2, 
               aes(lat2, long2, color = "val2"), 
               shape = 17, size = 11.5, alpha = 0) +
    scale_size_continuous(range = c(2, 12), breaks = pretty_breaks(4)) +
    scale_fill_distiller(direction = -1, palette = "RdYlBu", breaks = pretty_breaks(4)) +     
    scale_color_manual(values = "black", name = "Value\n") +
    labs(fill = NULL,
         size = NULL) +
    guides(fill = guide_legend(), 
           size = guide_legend(),
           color = guide_legend(order = 1)) +
   theme_minimal() +
   theme(legend.spacing.y = unit(-0.4, "cm"))