This tutorial shows GIS users how they can create public transport isochrones using ArcGIS Pro and the TravelTime add-in. We’ll have a look at two examples for creating isochrones in London, one from an x,y coordinate in Central London overlaid with public transport network data, and one using a public transport station in a popular office location showing a 45-minute public transport catchment area. This gives us an idea of the areas that lie within reach of 45 minutes using public transport.
What are isochrones?
Before diving into the examples, let’s take a minute and discuss isochrones. Isochrones show the area that is reachable from a starting point in a given amount of time, for a certain method of transport. These can replace distance radius areas (as created with Buffer tools in a GIS) to provide much more relevant catchment or trade areas.
Now, let’s have a look at some examples of public transport isochrone maps:
- Public transport isochrones around a popular office location in a big city give an idea of the size of the residential areas within short reach using different public transport modes, for example under 45 minutes. People living outside these catchment areas will need more time to reach this working destination than those living inside the catchment areas. Also, the TravelTime add-in enables you to differentiate between different hours of the day, so that it becomes possible to see how catchment areas change during the day, while maintaining the same time limit to reach a destination.
Here’s a public transport isochrone map for the London Bank station showing 15, 30 and 45 catchment areas:
- An isochrone map of 10/20/30 minute walking catchment areas around a random x,y (address) location in a residential area in a big city. By overlaying the isochrone with data from public transport stations nearby, we can analyze the different public transport stations that can be reached by an individual who wants to walk to any of these stations within a time frame from that address.
Here’s a map that shows the underground and train stations reachable within a 15-minute walk from Leicester Square in London:
- A map showing 10/20/30-minute walking catchment areas of an entire public transport network in a large city. Individual isochrones around different transport stations show the area where people are able to reach the public transport station from a given location and time frame. On a city level, it would be interesting to merge all different isochrones from the individual stations and identify areas that fall outside these catchment areas. City planners might want to investigate how extensions of existing public transport lines could serve such areas.
Here’s an example of areas falling outside of 20-minute walking catchment areas around all underground and train stations in London. We will see how to create this map later in the tutorial:
How to create isochrones in ArcGIS Pro
In this tutorial, we will use the TravelTime add-in for ArcGIS Pro to calculate isochrones around a location in Central London in order to see how many train and underground stations can be reached within a 15-minute walk. Next, we’ll show how to create a 45-minute public transport isochrone for a Canary Wharf station, located in a popular working location in London.
If you haven’t already installed the TravelTime add-in for Pro, you can get a free trial API key and download the extension here.
We’ll first generate an isochrone map showing the 45-minute public transport catchment area from Canary Wharf, a location in London where many people work.
We’ll use Canary Wharf station as our destination, which can be selected from our stations feature layer using the Select tool:
Running the tool shows a new feature layer with only one point, namely the Canary Wharf station.
Now, we can use this point feature and create another Quick Time Map, showing a 45-minute public transport catchment area. Because this time we are using a point layer as input instead of a random point on the map, we need to call the TravelTime Platform toolbox that is found in the Catalog window under Toolboxes, by first clicking the second item from the left in the TravelTime menu, as displayed below:
Next, click the Time Map Simple tool under Simplified and run the tool with the following input fields:
The results are added to the map automatically, showing the areas from where Canary Wharf station can be reached within a maximum of 45 minutes travelling by public transport:
To get an idea of public transport stations in different parts of London, we can create walking catchment areas for a given location in a residential area and see how many public transport stations are within reach of 10-15 minutes.
We can now run the TravelTime Quick Time Map tool from the ribbon interface and create isochrones for a central location in London, Leicester Square, WC2H 7DE. We fill in the required fields: we are interested in creating walking catchment areas for 10- and 15-minute journey times.
Next, we click on a location on the map displaying Central London and run the tool. After running the tool, the catchment areas are added to the map:
To get an idea of the public transport stations within reach, we can overlay this data with a feature layer named “london stations” from ArcGIS Online, that we can search through the Catalog window and choosing Portal:
Double-clicking the feature layer will automatically add it to the map window.
By running the Intersect tool, we can get a list of the train and metro stations that are inside our 15- and 10-minute catchment areas. We only need to define our input features and run the tool, which are our 15-minute catchment area and the London Stations. Looking at the resulting map and attribute table, we can see there are seven public transport stations to be found within our 15-minute walking catchment area. These are marked in a dark color on the map and their names are found in the corresponding attribute table of the tool results in the Station field:
For a public transport network analysis, we can also use the TravelTime add-in to create isochrones for all transport stations to display areas that are not reachable within a given travel time.
We can use the London stations layer and create 10/15/20 minute walking catchment areas using the TravelTime. To do this, we can open the Time Map Simple geoprocessing tool from the TravelTime_Platform from the Catalog Pane under Project:
This tool allows us to use the London stations point layer and create isochrones for all points at once. Running the tool multiple times (for 10-, 15- and 20-minute walking travel times) results in the following map:
We now need a polygon layer of the entire area of London so we can overlay it with the isochrones from Step 1. We bring in a feature layer called “statistical gis boundaries london” and run the Dissolve geoprocessing tool on the London_Ward_CityMerged layer inside it. Next, we use the Dissolve Boundaries tool on the result of that analysis so that we have a single polygon that represents the outer boundaries of London, which makes for a nicer visual output in a while:
Using the Erase geoprocessing tool, we can visualize the areas of London that fall outside of our different walking catchment areas. For the tool input we use the 20-catchment area polygon layer.
How is this approach different from what is currently possible within ArcGIS Pro?
The two isochrone maps from this tutorial were created using the TravelTime add-in for ArcGIS Pro. ArcGIS Pro also offers native functionality to create public transport isochrones through the Spatial Analyst extension. However, creating isochrones this way requires more work and offers less flexibility in combining multiple travel modalities than the TravelTime add-in, where you can choose your mode of transportation from a drop-down menu.
Before you can create a public transport isochrone map with the Spatial Analyst extension, ArcGIS requires an input network dataset that represents a public transport network of your choice, including the geographical locations of transit lines, stops and transit schedules. The spatial data needs to meet certain specifications, otherwise the network dataset can’t be used to calculate travel times among the transport network.
With the TravelTime add-in this has all been taken care of, so you can create isochrones directly from a given x,y coordinate by clicking on a map by choosing Quick Time Map from the ribbon interface, or from a feature layer by choosing from the Time Map Simple or Time Map Advanced from the TravelTime Platform toolbox.
Eric van Rees is a freelance technical writer. Besides blogging about the TravelTime add-in, he creates GIS tutorials, writes technical content for companies and is the news editor for GeoConnexion Magazine. You can find him on Twitter as @eric_van_rees.