AbstractThis vignette shows how to calculate and visualize accessibility in R using the
Accessibility metrics measure the ease with which opportunities, such as jobs, can be reached by a traveler from a particular location (Levinson and et al. 2020). One of the simplest forms of accessibility metrics is the cumulative-opportunities, which counts all of the opportunities accessible from each location in less than a cutoff time. Using a travel time matrix and information on the number of opportunities available at each location, we can calculate and map accessibility. This vignette shows how to do that in R using the
In this reproducible example, we will be using a sample data set for the city of Porto Alegre (Brazil) included in
r5r. We can compute accessibility in 5 quick steps:
Before we start, we need to increase the memory available to Java and load the packages used in this vignette
options(java.parameters = "-Xmx2G") library(r5r) library(sf) library(data.table) library(ggplot2) library(akima) library(dplyr)
To build a routable transport network with r5r and load it into memory, the user needs to call
setup_r5 with the path to the directory where OpenStreetMap and GTFS data are stored.
# system.file returns the directory with example data inside the r5r package # set data path to directory containing your own data if not using the examples <- system.file("extdata/poa", package = "r5r") data_path <- setup_r5(data_path, verbose = FALSE)r5r_core
In this example, we will be calculating the number of schools accessible by public transport within a travel time of up to 20 minutes. The sample data provided contains information on the spatial distribution of schools in Porto Alegre in the
With the code below we compute the median number of schools accessible considering multiple travel time estimates departing every minute over a 60-minute time window, between 2pm and 3pm.
# read all points in the city <- fread(file.path(data_path, "poa_hexgrid.csv")) points # routing inputs <- c("WALK", "TRANSIT") mode <- 1000 # in meters max_walk_dist <- 21 # in minutes travel_time_cutoff <- as.POSIXct("13-05-2019 14:00:00", departure_datetime format = "%d-%m-%Y %H:%M:%S") <- 60 # in minutes time_window <- 50 percentiles # calculate travel time matrix <- accessibility(r5r_core, access origins = points, destinations = points, mode = mode, opportunities_colname = "schools", decay_function = "step", cutoffs = travel_time_cutoff, departure_datetime = departure_datetime, max_walk_dist = max_walk_dist, time_window = time_window, percentiles = percentiles, verbose = FALSE) head(access) #> from_id percentile cutoff accessibility #> 1: 89a901291abffff 50 21 3 #> 2: 89a9012a3cfffff 50 21 0 #> 3: 89a901295b7ffff 50 21 6 #> 4: 89a901284a3ffff 50 21 1 #> 5: 89a9012809bffff 50 21 5 #> 6: 89a901285cfffff 50 21 3
The final step is mapping the accessibility results calculated earlier. The code below demonstrates how to do that, with some extra steps to produce a prettier map by doing a spatial interpolation of accessibility estimates.
# interpolate estimates to get spatially smooth result <- access %>% access.interp inner_join(points, by=c('from_id'='id')) %>% with(interp(lon, lat, accessibility)) %>% with(cbind(acc=as.vector(z), # Column-major order x=rep(x, times=length(y)), y=rep(y, each=length(x)))) %>% as.data.frame() %>% na.omit() # find results' bounding box to crop the map <- c(min(access.interp$x), max(access.interp$x)) bb_x <- c(min(access.interp$y), max(access.interp$y)) bb_y # extract OSM network, to plot over map <- street_network_to_sf(r5r_core) street_net # plot ggplot(na.omit(access.interp)) + geom_contour_filled(aes(x=x, y=y, z=acc), alpha=.8) + geom_sf(data = street_net$edges, color = "gray55", size=0.1, alpha = 0.9) + scale_fill_viridis_d(direction = -1, option = 'B') + scale_x_continuous(expand=c(0,0)) + scale_y_continuous(expand=c(0,0)) + coord_sf(xlim = bb_x, ylim = bb_y) + labs(fill = "Schools within\n20 minutes\n(median travel time)") + theme_minimal() + theme(axis.title = element_blank())
If you have any suggestions or want to report an error, please visit the package GitHub page.