003-maryland-maps.Rmd

---
title: "Map Maryland Congressional Elections"
output:
  html_notebook: default
  html_document: default
---

Simple maps of party percentages in Maryland congressional elections.

First compute the party percentages in each county for each election.

```{r setup, message = FALSE}
library(tidyverse)
library(USAboundaries)
library(leaflet)
library(forcats)
library(stringr)

md_raw <- read_csv("elections-data/congressional/county/congressional-counties-md.csv")
elections <- read_csv("elections-data/elections.csv")

md <- md_raw %>% 
  mutate(party = if_else(!party %in% c("Federalist", "Republican"), "Other", party)) %>% 
  group_by(election_id, county_ahcb) %>% 
  mutate(county_votes = sum(vote, na.rm = TRUE)) %>% 
  group_by(election_id, county_ahcb, party) %>% 
  summarize(vote = sum(vote, na.rm = TRUE)) %>% 
  group_by(election_id, county_ahcb) %>% 
  spread(party, vote, fill = 0) %>% 
  mutate(fed_percent = round(Federalist / (Federalist + Republican + Other), 3),
         rep_percent = round(Republican / (Federalist + Republican + Other), 3),
         oth_percent = round(Other / (Federalist + Republican + Other), 3),
         fed_diff = fed_percent - 0.5) %>% 
  left_join(elections, by = "election_id") %>% 
  filter(election_year >= 1796, 
         !is.na(county_ahcb)) %>%
  arrange(election_year) 
```

Functions to make the maps repeatable.

```{r}
popup_maker <- function(county, federalist, republican, other, fed_percent,
                        rep_percent, oth_percent) {
  str_c("<b>County: </b>", county, "<br>",
        "<b>Federalist: </b>", federalist, " (", fed_percent * 100, "%)<br>",
        "<b>Republican: </b>", republican, " (", rep_percent * 100, "%)<br>",
        "<b>Other: </b>", other, " (", oth_percent * 100, "%)<br>")
}

pal <- colorBin("PRGn", md$fed_diff, 7, pretty = TRUE)
  
make_md_map <- function(year) {
  md_counties <- us_counties(map_date = str_c(year, 08, 01, sep = "-"),
                             resolution = "high", states = "Maryland")
  df <- md %>% 
    filter(election_year == year) 
  
  md_counties@data <- md_counties@data %>% 
    mutate(id = as.character(id)) %>% 
    left_join(df, by = c("id" = "county_ahcb"))
  
  map <- leaflet(md_counties) %>% 
    addPolygons(stroke = TRUE, weight = 1, smoothFactor = 1, fillOpacity = 1,
                fillColor = ~pal(fed_diff), color = "black", opacity = 1,
                popup = ~popup_maker(county = str_to_title(name),
                                     federalist = Federalist,
                                     republican = Republican,
                                     other = Other,
                                     fed_percent = fed_percent,
                                     rep_percent = rep_percent,
                                     oth_percent = oth_percent)) %>% 
    addLegend("bottomright", pal = pal, values = md$fed_diff,
              title = "Federalist votes", 
              labFormat = labelFormat(suffix = "%",
              transform = function(x) { (x + 0.5) * 100}))
  cat("<h3>Maryland Congressional election of", year, "</h3>")
  print(map)
}
```

Make one map for each year.

```{r, results = "asis", fig.width=10}
walk(unique(md$election_year), make_md_map)
```