R语言：为ggplot2绘图及图例添加矩形边框

Hey there! As someone new to R, it’s totally normal to hit snags with ggplot syntax—let’s work through your polygon plotting issue step by step. I notice your code cuts off mid-way through the scale_fill_manual call, which is likely one of the key problems. Here’s how to fix and debug this:

1. Fix the Incomplete scale_fill_manual Code #

Your current code has a duplicate values=c( and is unfinished. This parameter needs a full set of colors mapped to your ALG categories. For example:

• If ALG has named categories (like "Good", "Fair", "Poor"), map each to a color explicitly:

  scale_fill_manual(
    "Aquatic Life Designated\nUse 2014 Assessment",
    values = c("Good" = "#2ecc71", "Fair" = "#f39c12", "Poor" = "#e74c3c")
  )
  

• If you just need to assign colors in the order of ALG’s factor levels, use a simple vector:

  scale_fill_manual(
    "Aquatic Life Designated\nUse 2014 Assessment",
    values = c("#2ecc71", "#f39c12", "#e74c3c")
  )
  

2. Verify Your Data Format #

Polygons in ggplot rely on properly structured data—double-check these details:

• Ensure long, lat are numeric columns (not character strings) in your df data frame.
• The group column must correctly group all points that belong to the same polygon. If groups are misassigned, your shapes will render incorrectly or overlap.
• Confirm ALG is a categorical variable (convert it with df$ALG <- factor(df$ALG) if it’s numeric) so ggplot can map colors to distinct groups.

3. Simplify to Test the Base Plot #

Before adding titles and custom scales, test if the core polygon plot works:

# Minimal working example to check if polygons render
graph1 <- ggplot() +
  geom_polygon(data = df, aes(x = long, y = lat, group = group, fill = ALG), colour = "black") +
  coord_equal()

print(graph1)

If this basic plot shows up, you can safely add back your ggtitle, xlab, ylab, and fixed scale_fill_manual layer.

4. Troubleshoot Common Errors #

• "Object not found": Double-check that all column names (long, lat, group, ALG) match exactly what’s in your df (R is case-sensitive!).
• Distorted/missing polygons: This usually means your group variable is incorrect. Use table(df$group) to check if each polygon has a unique group ID.
• No fill colors showing: If ALG is a continuous variable, use scale_fill_continuous() instead of scale_fill_manual().

内容的提问来源于stack exchange，提问作者NBE