Add NA value to ggplot legend for continuous data map

Question

I\'m using ggplot to map data values to a (fortified) SpatialPolygonsDataFrame, but many of the polygons have NA values because there is no data available.

I used na.va

Answer 1

you can replace your NAs with 0 using

data[is.na(data)] <- 0

that way your nas will be replaced by zero and yout legend will show "0s"

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Answer 2

Try this:

ggplot(all your info) + geom_point(na.rm = TRUE) + geom_line(na.rm = TRUE)

Answer 3

You could make use of the behavior of ggplot which creates a legend when specifying certain aesthetics within aes()
I am creating some dummy data and am using geom_map instead of geom_polygon, which I find easier. You can then use override.aes to specify the fill of the legend key with the NA value. You can then easily rename the legend etc.

library(tidyverse)

worldData <- map_data('world') %>% fortify()
india.df <- data.frame(region = 'India', Area_pct = 2, stringsAsFactors = FALSE) %>% right_join(worldData, by = 'region')

na.value.forplot <- 'white'

ggplot() +
  geom_map(data = india.df, map = india.df, aes(x = long, y = lat, fill = Area_pct, map_id = region, color = 'NA')) +
  scale_fill_gradient(low="orange2", high="darkblue", na.value = na.value.forplot) +
  scale_color_manual(values = 'black', labels = 'Missing value') +
  guides(color = guide_legend(override.aes = list(fill = na.value.forplot)))
#> Warning: Ignoring unknown aesthetics: x, y

^{Created on 2019-07-18 by the reprex package (v0.3.0)}