1. Introduction

An isochrone shows all areas reachable from a place within a maximum travel time. This vignette uses the r5r package and the Porto Alegre (Brazil) sample data included in it to calculate and map public transport isochrones from the city’s central bus station at several travel time thresholds. r5r::isochrone() builds both polygon- and line-based isochrones; we cover both.

Warning: to count opportunities (e.g. jobs, schools or hospitals) within each isochrone, we strongly recommend NOT using isochrone(). The Accessibility vignette shows much more efficient ways.

2. Build routable transport network with `build_network()`

Increase Java memory and load libraries

Set Java memory before loading the packages (why).

options(java.parameters = "-Xmx2G")

library(r5r)
library(sf)
library(data.table)
library(ggplot2)

build_network() takes the directory holding the OpenStreetMap and GTFS data:

# system.file returns the directory with example data inside the r5r package
# set data path to directory containing your own data if not running this example
data_path <- system.file("extdata/poa", package = "r5r")

r5r_network <- build_network(data_path)

3. Calculating and visualizing isochrones

3.1 Polygon-based isochrones

Polygon-based isochrones are the most common: set polygon_output = TRUE. The polygons are built on a regular grid of Web Mercator pixels whose resolution is set by zoom. Higher zooms give more detailed isochrones but take longer, and may fail with an error in large networks. The default, 10, uses cells of 153 m at the Equator.

Below, isochrones use the median travel time of departures every minute over a 60-minute window (2pm to 3pm).

# read all points in the city
points <- fread(file.path(data_path, "poa_hexgrid.csv"))

# subset point with the geolocation of the central bus station
central_bus_stn <- points[291,]

# isochrone intervals
time_intervals <- seq(0, 100, 10)

# routing inputs
mode <- c("WALK", "TRANSIT")
max_walk_time <- 30      # in minutes
time_window <- 60        # in minutes
departure_datetime <- as.POSIXct("13-05-2019 14:00:00",
                                 format = "%d-%m-%Y %H:%M:%S")

# calculate travel time matrix
iso1 <- r5r::isochrone(
  r5r_network,
  origins = central_bus_stn,
  mode = mode,
  polygon_output = TRUE, 
  cutoffs = time_intervals,
  departure_datetime = departure_datetime,
  max_walk_time = max_walk_time,
  time_window = time_window,
  progress = FALSE,
  zoom = 10
  )

isochrone() works like travel_time_matrix(), but with polygon_output = TRUE it returns an sf data.frame with one POLYGON/MULTIPOLYGON per origin, cutoff and percentile:

head(iso1)

Mapping the isochrones:

# extract OSM network
street_net <- street_network_to_sf(r5r_network)
main_roads <- subset(street_net$edges, street_class %like% 'PRIMARY|SECONDARY')
  
colors <- c('#ffe0a5','#ffcb69','#ffa600','#ff7c43','#f95d6a',
            '#d45087','#a05195','#665191','#2f4b7c','#003f5c')

ggplot() +
  geom_sf(data = iso1, aes(fill=factor(isochrone)), color = NA, alpha = .7) +
  geom_sf(data = main_roads, color = "gray55", size=0.01, alpha = 0.2) +
  geom_point(data = central_bus_stn, aes(x=lon, y=lat, color='Central bus\nstation')) +
  scale_fill_manual(values = rev(colors) ) +
  scale_color_manual(values=c('Central bus\nstation'='black')) +
  labs(fill = "Travel time\n(in minutes)", color='') +
  theme_minimal() +
  theme(axis.title = element_blank())

3.2 Line-based isochrones

For line-based isochrones, set polygon_output = FALSE (no zoom needed). The output is a LINESTRING sf data.frame.

# calculate travel time matrix
iso2 <- r5r::isochrone(
  r5r_network,
  origins = central_bus_stn,
  mode = mode,
  polygon_output = FALSE, 
  cutoffs = time_intervals,
  departure_datetime = departure_datetime,
  max_walk_time = max_walk_time,
  time_window = time_window,
  progress = FALSE
  )

head(iso2)

Mapping the isochrones:

ggplot() +
  geom_sf(data = iso2, aes(color=factor(isochrone)), alpha = .7) +
  scale_color_manual(values = rev(colors) ) +
  geom_point(data = central_bus_stn, aes(x=lon, y=lat), color='black') +
  labs(color = "Travel time\n(in minutes)") +
  theme_minimal() +
  theme(axis.title = element_blank())

Cleaning up after usage

Stop the network and run Java’s garbage collector to free the memory it used:

r5r::stop_r5(r5r_network)
rJava::.jgc(R.gc = TRUE)

If you have any suggestions or want to report an error, please visit the package GitHub page.

Isochrones