Introduction
Today I am pleased to announce that the latest version of choroplethr is now available on CRAN. To install it you can type the following from an R console:
install.packages(“choroplethr”) library(choroplethr)
You only need to install the package once. But in each session that you want to use choroplethr you need to type the library command.
The most requested feature has been to give users more control over how maps are rendered. Version 1.2 provides three functions (get_acs_df, bind_df_to_map and render_choropleth) to address this. Here are 4 examples of using those functions to extract meaning from maps.
Example 1: Showing states with population over 1M
The choroplethr_acs function, available since version 1.0, makes it easy to create maps from ACS data. Consider the example of creating a map of the population of US states:
# see ?choroplethr_acs for an explanation of the parameters
choroplethr_acs("B01003", "state")
This map is very informative, but no map can tell you everything. For example, in this map you cannot tell which states have a population above or below 1 million residents. The new features in choroplethr make this easy:
Use get_acs_df to get an ACS table as a data.frame.
df = get_acs_df("B01003", "state")
# Use bind_df_to_map to bind the data to a map
df.map = bind_df_to_map(df, "state")
# change the population from a number to a factor
# which shows whether the value is above or below 1M
library(Hmisc) # for cut2
df.map$value = cut2(df.map$value, cuts=c(0,1000000,Inf))
# use render_choropleth to render the resulting object
render_choropleth(df.map, "state", "States with a population over 1M", "Population")
Example 2: Comparing States and Counties with Populations over 1M
These features open a new door for analysis. As a small example, let’s create a map that compares states with populations over 1M with counties that have populations over 1M:
# States with greater than 1M residents
library(Hmisc) # for cut2
df = get_acs_df("B01003", "state") # population
df.map = bind_df_to_map(df, "state")
df.map$value = cut(df.map$value, cuts=c(0, 1000000, Inf))
state.pop = render_choropleth(df.map, "state", "States with a population over 1M", "Population")
# Counties with greater than 1M residents
df = get_acs_df("B01003", "county") # population
df.map = bind_df_to_map(df, "county")
df.map$value = cut(df.map$value, cuts=c(0, 1000000, Inf))
county.pop = render_choropleth(df.map, "county", "Counties with a population over 1M", "Population")
library(gridExtra)
grid.arrange(state.pop, county.pop, nrow=2, ncol=1)
Example 3: “The 1%”
One of the most talked about demographic features on the news today is “The 1%”. This refers to individuals whose income is in the 99th percentile in a given year. In this example we use the new features in choroplethr to highlight counties where the median family income is in the 99th percentile of all counties nationwide:
df = get_acs_df("B19113", "county") # median family income
df.map = bind_df_to_map(df, "county")
df.map$value = cut2(df.map$value, cuts=c(min(df$value), quantile(df$value, 0.99), max(df$value)))
render_choropleth(df.map, "county", "Counties with the Top 1% Median Family Income")</pre>
Example 4: ZIPs in California
As a final example, let’s consider trying to identify ZIP codes in California where the median age is between 20 and 30. (In this post I use the word ZIP code, which is not technically correct, because it’s more widely understood. The correct term to use here is ZCTA; I explain why in this blog post.) Note that we can simply remove ZIPs which we are not interested in.
df = get_acs_df("B01002", "zip") # median age
df.map = bind_df_to_map(df, "zip")
ca_zips = render_choropleth(df.map, "zip", "CA ZIPs", "Median Age", states="CA")
df = df[df$value >= 20 & df$value <= 30, ]
df.map = bind_df_to_map(df, "zip")
ca_zips_20s = render_choropleth(df.map, "zip", "CA ZIPs with median age between 20 and 30", "Median Age", states="CA")
grid.arrange(ca_zips, ca_zips_20s, nrow=2, ncol=1)
Conclusion
Hopefully these new features allow you to do more interesting work with visualizing and analyzing spatial information. If you would like to share any of you work, please feel free to contact me on twitter or post on the choroplethr forum.
