Geographical heat map in R

Question

i want to create a map of the US in R with the states color coded in a heat map type of way based on a metric. I know how to do this using the googleVis api but i can\'t us

Answer 1

There is a complete example in the ggplot2 package, see ?map_data.

library(ggplot2)
example(map_data)

Answer 2

Code

# Transform dataset to correct format
crimes <- data.frame(state = tolower(row.names(USArrests)), USArrests)
crimes

#  Map data   
#  install.packages("maps") remember to install these two packages if you  
#  install.packages("mapproj") do not have them yet

library(mapproj)
library(maps)

states_map <- map_data("state")
states_map

# Merge datasets together 
crime_map <- merge(states_map, crimes, by.x = "region", by.y = "state")

# After merging, the order has changed, which leads to polygons drawn 
# in the incorrect order. Let's sort it 
crime_map

library(dplyr) # for arrange() function 

# Sort by group, then order 
crime_map <- arrange(crime_map, group, order)
crime_map

# Now data can be plotted
library(ggplot2)

plot1 <- ggplot(crime_map, aes(x = long, y = lat, group = group, fill = Assault)) + 
                    geom_polygon(colour = "black") + 
                    coord_map("polyconic")

plot1

# Add title 
plot1 <- plot1 + 
                ggtitle("                       Proportion of crimes in the USA")

plot1

# Improve on colours 
plot1 <- plot1 + 
    scale_fill_gradient2(low = "#559999", mid = "grey", high = "#BB650B",
                                                    midpoint = median(crimes$Assault))
plot1

# If you want white transparent backgroud only
plot1 <- plot1 + 
         theme_void()

plot1

# Note: if RStudio gives you this error when ploducing plot, then use this and try 
# again
devAskNewPage(ask = FALSE)

# Special thanks to Winston Chang and other ggplot developers at RStudio who made made 
#  many of these codes 

Answer 3

(hopefully answer may still be helpful for somebody)

RevolutionAnalytics has excellent example of map visualization using spplot() function. Here's image from there:

Answer 4

There is a population-driven cloropleth example in the UScensus2000tract package.