Trying to make a map with leaflet, pls help!

[amal]

This is my first time asking for help so please let me know if I did something wrong. I want to create a map of evictions by county in Ohio. I am using data from the Princeton Eviction lab that I downloaded. I really have no idea how to use it. The geojson file has several features. It has a bunch of variables for different years. For instance, er-01 means the eviction rate in 2001. er-16 means the eviction rate in 2016. The data is from 2000 until 2016. I would like to plot this eviction rate variable for each year. Please help! The following code is something I tried, but I am not sure how to add a legend. Is there an easier way to do this? How can I plot for just one variable and do it for every year?

```{r}
library(leaflet)
library(geojsonio)
library(utils)
library(tidyverse)

download.file("https://raw.githubusercontent.com/amalabdi/milestone_8/master/counties.geojson", "counties.geojson")
geojson <- readLines("counties.geojson", warn = FALSE) %>%
  paste(collapse = "\n") %>%
  fromJSON(simplifyVector = FALSE)

# Default styles for all features
geojson$style = list(
  weight = 1,
  color = "#555555",
  opacity = 1,
  fillOpacity = 0.8
)

# Er-03 is the the eviction rate in 2003
evictionrate <- sapply(geojson$features, function(feat) {
  feat$properties$`er-03`
})

# Add a properties$style list to each feature
geojson$features <- lapply(geojson$features, function(feat) {
  feat$properties$style <- list(
    fillColor = feat$properties$`er-03`
  )
  feat
})

# Add the now-styled GeoJSON object to the map
leaflet() %>% addGeoJSON(geojson) 

[williaml]

I haven't done much with geojson but maybe this will help. https://rstudio.github.io/leaflet/json.html

I couldn't get the fromJSON to work, but it works with the RJSONIO library.

[Nate]

My baseline strategy for spatial data in R is to get it into sf objects as fast as possible.

You can read geoJSON links directly with sf::read_sf()

library(sf)

sf <- read_sf(
  "https://raw.githubusercontent.com/amalabdi/milestone_8/master/counties.geojson")

Picking out a good color column and a pretty palette:

library(leaflet)

pal_val <- sf$er.03
pal <- colorNumeric("viridis", pal_val)

Then just stack it all together, with some nice map tiles for flair.

leaflet(sf) %>%
  addProviderTiles(providers$Stamen.Toner) %>%
  addPolygons(color = ~pal(pal_val),
              fillColor = ~pal(pal_val)) %>% 
  addLegend(pal = pal, values = pal_val)

[amal]

Thank you so much!! I have been stuck for so long. Is there any way to use addCircleMarkers to display circles whose sizes correspond to the eviction rate (aka er-03)? I am not sure where to begin with calculating centroids so it plots in the middle of each county or how to pull the latitude and longitude for addCircleMarkers.

[Nate]

Again sf is the way.

Now that you have an sf object with the polygons for each of the 88 counties in Ohio. You use sf::st_centroid() to convert those polygons into center points.

sf_centers <- sf %>%
dplyr::mutate(geometry = st_centroid(geometry))

And in leaflet land size is controlled by the radius argument.

leaflet(sf_centers) %>%
addProviderTiles(providers$Stamen.Toner) %>%
addCircleMarkers(radius = ~er.03)

If you want to adjust the sizing of the circle-markers you would adjust the er.03 value with some mathematical operation (addition, multiplication or exponentiation) instead of the pal idea you have to use for coloring.