Geospatial

Continuous Outcome

• {ggmap} Dot map

  • Example: Does Price vary by location?

  • In your data, find the min and max latitude and longitude to specify a bounding box

    library(ggmap)
    bbox <- c(left = min_longitude, 
              bottom = min_latitude, 
              right = max_longitude, 
              top = max_latitude)
    map_tiles <- get_stamenmap(bbox, zoom = 13)

  • (Optional) Aggregate some of the data (i.e. dots)

    agg_dat <- dat %>%
        group_by(latitude = round(latitude, 2),
                longitude = round(longitude, 2)) %>%
        summarize(avg_outcome = mean(numeric_outcome),
                  n = n())

  • scale_size_continuous adjusts the range of dot sizes. This range makes them a little smaller.
    

    ggmap(map_tiles) +
        geom_point(aes(longitude, latitude, 
                       size = n, 
                       color = avg_outcome), 
                   data = agg_dat) +
        scale_color_gradient2(low = "blue", 
                              high = "red", 
                              midpoint = midpoint_value_of_numeric_outcome,
                              trans = "log10", 
                              labels = dollar) +
        scale_size_continuous(range = c(0.5, 4)) +
        theme_map() +
        labs(color = "avg_outcome", 
             size = "n")

    • trans and labels are for the legend (I think).