length(table(nhgis$STATE))
#> [1] 28

#     A:  Twenty‐Eight (28)

table(nhgis$STATE)
#> 
#>              Alabama   Arkansas Territory          Connecticut 
#>                    1                    1                    1 
#>             Delaware District Of Columbia    Florida Territory 
#>                    1                    1                    1 
#>              Georgia             Illinois              Indiana 
#>                    1                    1                    1 
#>             Kentucky            Louisiana                Maine 
#>                    1                    1                    1 
#>             Maryland        Massachusetts   Michigan Territory 
#>                    1                    1                    1 
#>          Mississippi             Missouri        New Hampshire 
#>                    1                    1                    1 
#>           New Jersey             New York       North Carolina 
#>                    1                    1                    1 
#>                 Ohio         Pennsylvania         Rhode Island 
#>                    1                    1                    1 
#>       South Carolina            Tennessee              Vermont 
#>                    1                    1                    1 
#>             Virginia 
#>                    1
#     A: In 1830, there were not any other states yet! Every decennial census is a 
#        historical snapshot, and NHGIS provides census counts just as they were 
#        originally reported without "filling in" any information for newer areas.

nhgis <- nhgis %>%
  mutate(total_pop = ABO001 + ABO002 + ABO003 + ABO004 + ABO005 + ABO006)

nhgis %>%
  as.data.frame() %>%
  select(STATE, total_pop) %>%
  arrange(desc(total_pop)) %>%
  slice(1:5)
#> # A tibble: 5 x 2
#>            STATE total_pop
#>            <chr>     <int>
#> 1       New York   1913006
#> 2   Pennsylvania   1348233
#> 3       Virginia   1211405
#> 4           Ohio    937903
#> 5 North Carolina    737987

#     A: New  York

nhgis <- nhgis %>%
  mutate(slave_pop = ABO003 + ABO004)

nhgis %>%
  as.data.frame() %>%
  select(STATE, slave_pop) %>%
  arrange(desc(slave_pop)) %>%
  slice(1:5)
#> # A tibble: 5 x 2
#>            STATE slave_pop
#>            <chr>     <int>
#> 1       Virginia    469757
#> 2 South Carolina    315401
#> 3 North Carolina    245601
#> 4        Georgia    217531
#> 5       Kentucky    165213

#     A: Virginia 

nhgis <- nhgis %>%
  mutate(pct_slave = slave_pop / total_pop)

nhgis %>%
  as.data.frame() %>%
  select(STATE, pct_slave) %>%
  filter(pct_slave %in% c(min(pct_slave, na.rm = TRUE), max(pct_slave, na.rm = TRUE)))
#>            STATE pct_slave
#> 1        Vermont 0.0000000
#> 2 South Carolina 0.5426861

#     A: South Carolina (54.27%) and Vermont (0.00%)

nhgis %>%
  as.data.frame() %>%
  filter(pct_slave > 0.5) %>%
  select(STATE, slave_pop, total_pop, pct_slave)
#>            STATE slave_pop total_pop pct_slave
#> 1 South Carolina    315401    581185 0.5426861
#> 2      Louisiana    109588    215529 0.5084606

nhgis %>%
  as.data.frame() %>%
  filter(STATE %in% c("New York", "New Jersey")) %>%
  select(STATE, slave_pop, total_pop, pct_slave) 
#>        STATE slave_pop total_pop    pct_slave
#> 1   New York        75   1913006 3.920531e-05
#> 2 New Jersey      2254    320823 7.025681e-03

#     A: Possibilities: Did you know some states had more slaves than free persons? Did
#        you know that some “free states” were home to substantial numbers of slaves?

cat(ipums_file_info(nhgis_ddi, "conditions"))
#>  
#> All persons are granted a limited license to use this documentation and the
#> accompanying data, subject to the following conditions:
#> 
#> * Publications and research reports employing NHGIS data (either tabular or GIS)
#>   must cite it appropriately. The citation should include the following:
#> 
#>     Steven Manson, Jonathan Schroeder, David Van Riper, and Steven Ruggles. 
#>     IPUMS National Historical Geographic Information System: Version 12.0 [Database]. 
#>     Minneapolis: University of Minnesota. 2017. 
#>     http://doi.org/10.18128/D050.V12.0
#> 
#> * Publications and research reports employing school attendance areas data
#>   (either tabular or GIS) must cite it appropriately. The citation should
#>   include the following:
#> 
#>     The College of William and Mary and the Minnesota Population Center.
#>     School Attendance Boundary Information System (SABINS): Version 1.0.
#>     Minneapolis, MN: University of Minnesota 2011.
#> 
#> * For policy briefs or articles in the popular press, we recommend that you cite the use of NHGIS data as follows:
#> 
#>     IPUMS NHGIS, University of Minnesota, www.nhgis.org.
#> 
#> * If possible, citations involving school attendance areas should also include
#>   the URL for the SABINS site:
#> 
#>     http://www.sabinsdata.org/.
#> 
#> In addition, we request that users send us a copy of any publications, research
#> reports, or educational material making use of the data or documentation.
#> Printed matter should be sent to:
#> 
#>     NHGIS
#>     Minnesota Population Center
#>     University of Minnesota
#>     50 Willey Hall
#>     225 19th Ave S
#>     Minneapolis, MN 55455

#     A: Minnesota Population Center. National Historical Geographic Information
#        System: Version 11.0 [Database]. Minneapolis: University of Minnesota. 2016.
#        http://doi.org/10.18128/D050.V11.0.

#     A: (You can also send questions you may have about the site. We’re happy to help!)
#     nhgis@umn.edu

# Note the function `geom_sf()` is currently only in the development version, 
# so you may need to update ggplot2 to run using 
#   devtools::install_github("tidyverse/ggplot2")
library(ggplot2)
if ("geom_sf" %in% getNamespaceExports("ggplot2")) {
  ggplot(data = nhgis, aes(fill = pct_slave)) +
    geom_sf() + 
    scale_fill_continuous("", labels = scales::percent) + 
    labs(
      title = "Percent of Population that was Enslaved by State",
      subtitle = "1830 Census",
      caption = paste0("Source: ", ipums_file_info(nhgis_ddi, "ipums_project"))
    )
}