Public Transit in ArcGIS
Public transit (like buses and subways) serves the people of a city by providing access to jobs, education, shopping, healthcare, recreation, and more. Traffic congestion, climate change, and the evolving economy and population of cities have created a greater need than ever to understand how well transit is serving these needs.
Want to figure out who is underserved by transit, calculate job accessibility in your city, or identify a good place in an urban area to expand your business so it’s easy to get to? How about viewing a map of areas within a short walk of a transit stop?
Explore this Story Map to learn how you can utilize ArcGIS to answer questions like these.
Questions
Specifically, we will consider the following:
- Who does the transit system serve?
- How well are people served by transit?
- How easily can people access important destinations by transit?
We will use tools in ArcGIS and GTFS public transit data to answer these questions.
Resources and tools
Throughout this Story Map, we will include links to tools and other resources you can use to make maps similar to the ones shown here. All of these resources can be accessed directly from http://esriurl.com/transittools , and you can learn how to do analyses like this yourself by watching our tutorial video series .
Data
The General Transit Feed Specification (GTFS) is the only worldwide standard format for public transit stops, routes, and schedules. The advent of GTFS has opened up a world of new possibilities for analysis of and with public transit data in ArcGIS.
GTFS data for this Story Map is provided by MARTA, the public transit agency in Atlanta, Georgia, USA.
Who does the transit system serve?
A typical fixed-route transit system serves only the people and areas within a short distance of transit stops. To answer the question "Who does my transit system serve?", we need to answer some sub-questions:
- Where are the transit stops and lines?
- What geographic area is served by the transit system?
- What are the demographic characteristics of the area covered?
Where are the transit stops and lines?
The most fundamental and important thing we need to do, of course, is to simply view the locations of transit stops and lines in a map.
This map shows MARTA lines and stops in Atlanta, Georgia, USA. Click a line or stop to see its name.
If you don't already have transit stops and lines in a geographic format, you can use your GTFS data to generate data that ArcGIS can read. Use the GTFS Stops To Features and GTFS Shapes To Features tools in ArcGIS Pro to convert your GTFS data into layers in the map.
What geographic area is served by the transit system?
Once we know the location of the stops and lines, we probably want to know which areas of town have easy access to these stops and lines. Many agencies consider the area within a quarter mile of transit service to have good access to the system.
But how should we (and how should we not) calculate this area served? The map here is a preview of what we want to create. Keep reading to find out what this means and how it was created.
To find the area served by your transit system, the first thing you might be tempted to do is to create a quarter-mile buffer around the transit lines.
Please don’t do this!
Line buffers are inaccurate. People can’t just jump on or off the bus or train as it rolls along. They have to use the designated stops. If you buffer around the lines, you will drastically overestimate the area served.
The map shows MARTA Route 25 with a quarter-mile line buffer around it. It looks nice, but as we'll see, it's not very accurate.
The next thing you might be tempted to do is to create circular buffers of a quarter mile or so around your transit stops.
Please don't do this either!
Circular buffers are inaccurate. Although this is a little better than line buffers, it’s still not great. After all, people usually can’t walk in a straight line in every direction from the transit stop. They are constrained, for the most part, to walk along the streets or sidewalks. If you have to zig-zag through a warren of streets, your quarter mile will be expended before you reach a quarter mile as the crow files. You might also run into geographic or man-made features in the way, like a river or highway with no pedestrian crossing.
So, circular buffers around stops can also drastically overestimate the area within a short walk of each stop, and, in turn, the area served by your transit system as a whole.
So what should you do? The solution is to use the Service Area tool.
Do this instead!
Service Areas, also known as isochrones or drive time polygons (or walk distance polygons, in our case) show the area reachable from a given location within a time or distance limit, assuming the traveler is constrained to a road network and subject to certain rules, like speed limits, one ways, or roads closed to pedestrians.
The map compares the quarter-mile circular buffer and Service Area for this bus stop. There's a big difference!
In this example, the circular buffer covers an area of about 0.20 square miles, and the Service Area covers an area of about 0.13 square miles. The circular buffer overestimates the reachable area by about 57%!
Let's revisit Route 25 from earlier. If you calculate a Service Areas around each transit stop, you will achieve a much more accurate estimate of the area served by the transit line.
In this example, the line buffer has an area of about 4.0 square miles, while the Service Areas around stops have an area of about 1.7 square miles. The line buffer overestimates the area with access to this transit line by 131%!
You can use Service Areas to calculate the coverage of your entire transit system. The results will be more accurate than line buffers or circular buffers around stops.
The map here shows quarter-mile Service Areas around all the MARTA stops in Atlanta, Georgia, USA. It shows the area served by the transit system.
To create Service Areas for your transit stops, you first need an accurate feature class of your transit stop locations. If you’re working with GTFS data, you can create a feature class of stops using the GTFS Stops To Features tool in ArcGIS Pro.
Once you have your stops, you can use ArcGIS Pro or ArcGIS Online to calculate Service Areas around the stops (in ArcGIS Online, it’s called “Create Drive-Time Areas”). Read through the documentation and tutorials linked here to learn how to set up and run a Service Area analysis with the appropriate settings.
What are the demographic characteristics of the area covered?
The purpose of transit isn't to serve area but to serve people. Once you have calculated the coverage of your transit system, you can do some demographic analysis to find out more about the people who live in that area.
Click a stop in the map here to see the demographics of the people who live near the stop.
The Enrich tool in ArcGIS Pro or ArcGIS Online makes creating a map like this particularly easy. You can choose from hundreds of demographic variables from Esri’s extensive demographic content , and the tool will summarize this demographic information for whatever polygons you feed it (like your transit system’s Service Area).
Actually, if the only thing you’re interested in is the demographics of the populations within a walk distance of each stop, and you don’t care about visualizing your transit system’s service area in a map, you can just enrich the stops directly without generating the polygons first. The Enrich tool will calculate Service Areas on the fly if you choose “Walking time” or “Walking distance” in the “Define areas to enrich” parameter.
How well are people served by transit?
We've shown how to find out where and who can easily access the transit system. But how good is this access? How well are people served? Not all transit service is created equal. The frequency of service matters a lot. We need to know how often each stop is visited.
This is where the true power of public transit schedule data comes in. We can use the schedules to count the number of times each stop is visited during a time window. You can do this with the Calculate Transit Service Frequency tool in ArcGIS Pro.
This map shows the MARTA transit stops color-coded by frequency of transit service during morning rush hour on a weekday (6:30 AM - 9:30 AM).
Click a stop in the map to see how many times per hour a bus (or train) visits it during the morning rush period.
Some areas have more frequent service than others.
Recall how we calculated the area served by a transit system. We created Service Areas showing the area within a quarter mile walk of all the transit stops. This is informative, but we can do better! We can color-code the areas by how frequently they are served.
This map shows the area served by MARTA stops color-coded by transit frequency.
The time of day matters, too. Click on each time period below to see how different times affect service frequency.
Note that some areas are served by more than one stop. This map shows the number of transit trips available within a quarter mile walk of these areas, even if the trips are available at different stops. If the same trip (the same bus or train) visits two stops within a quarter mile of the area, the trip is only counted once.
Some destinations have more frequent service than others.
We might want to consider the frequency of transit service available at specific points of interest. For example, you could find out how many trips per hour are available at supermarkets, health clinics, schools, or a couple of apartments you’re thinking about renting.
This map shows the frequency of transit service at Atlanta-area supermarkets during the daytime on a Saturday (9:30 AM - 3:30 PM). Click a supermarket in the map to see how many times per hour a bus (or train) visits it during the daytime on a Saturday.
Some parcels have more frequent service than others. You could take your point-of-interest analysis to the extreme and calculate the transit frequency available to each individual parcel in your city.
This map shows the frequency of transit trips available at each individual parcel in the City of Atlanta during the morning rush period on a weekday (6:30 - 9:30 AM). Click on a parcel to view how many transit stops are available within a .25 mile walking distance and how many transit trips are made per hour during the morning rush period. Use the search box in the map to search for a specific address.
Suppose there’s a bus stop right outside Jerry’s house. It’s very easy and convenient for Jerry to walk out his front door to the bus stop to wait for a bus. Suppose there’s a bus stop right outside Tom’s house, too. But, whereas a bus visits Jerry’s stop every 10 minutes, Tom’s stop only gets a bus once every hour. Although it’s equally easy for Jerry and Tom to get to a bus stop, Jerry is almost certainly better served by the transit system because he has a lot more opportunities to actually get on the bus and travel away. He’s less likely to be late for work if he misses his bus, and he doesn’t have to plan his errands quite so carefully.
Is Tom’s neighborhood underserved by the public transit system? Are there disparities in how well Jerry’s and Tom’s respective demographic or socioeconomic groups are served? Is Jerry’s house worth more than Tom’s because of its better transit service? Is Tom more likely to drive his car to work than Jerry? Combine your transit frequency analysis with other data to answer questions like these.
How easily can people access important destinations by transit?
Frequent, nearby transit service isn't useful if that service doesn't take you valuable destinations, like your job, your school, the grocery store, the doctor's office, the airport, etc. We need to understand where the transit service goes.
If we can do this for an entire city, we can find out whether some areas have better access to important destinations than others, and we can use this information to understand other trends and to correct disparities.
Recall that a Service Area shows the area reachable from a certain point within a particular distance or time limit. The map here shows a 15-minute walk time Service Area around a location in Atlanta. If you started walking from this point, you could reach any part of the highlighted area in 15 minutes or less.
What if we could take transit?
There is a lot of transit service in this area of town. We want to understand not just where we could walk to within 15 minutes, but where we could travel to if we used transit as well.
We can reach more area using transit. See how the Service Area expands when we consider where we can reach within 15 minutes by walking and transit. The larger polygon is a walk + transit Service Area.
You can create a walk + transit Service Area like this in ArcGIS Pro Network Analyst .
Why is there a little disconnected blob of reachable area to the southwest? Because I can only get the bus off at designated stops. Most of my 15-minute travel time has been been expended already when I get off the bus, leaving me only a few minutes to walk from the stop to wherever I'm going. It's normal and expected to see disconnected areas like this when making Service Areas with transit.
Time of day matters. The available transit changes depending on the time of day.
The previous map showed the walk + transit Service Area if I left at 10:08 AM. But transit runs on a schedule, so the available transit service is different depending on the time of day I want to travel. Some buses might not be running, or I might experience different wait times.
This map shows the walk + transit Service Area at 10:09 AM, just one minute later than the previous map. It looks very different! What happened? Why is the area to the south no longer reachable?
I just missed my bus.
Where does the transit go? There is no single answer. It depends on the time of day. The reachable area varies a lot.
The video here shows the walk + transit Service Area around our location in Atlanta for each start time between 10:00 AM and 11:00 AM.
You can create walk + transit Service Areas over a time window using the Prepare Time Lapse Polygons tool, part of the downloadable Transit Network Analysis Tools tool suite.
The travel time between two points varies a lot.
Consider a single origin (like your house) and a single destination (like your job). The time it takes to travel between the origin and the destination varies based on the available transit service.
From this graph, you can see that the maximum travel time between this origin and destination is just under an hour. This is how long it would take if you just walked the whole way. However, at certain times of day, transit service is available that reduces the travel time to about 30 minutes.
You can calculate walk + transit travel times between origins and destinations with an Origin-Destination Cost Matrix analysis and a transit-enabled network dataset created in ArcGIS Pro.
Let’s consider a large number of origins and destinations. For example, rather than just your house and your job, let’s consider every house and every job. To make this manageable, we'll use census blocks to represent this and calculate the travel time from each census block centroid to every other census block centroid.
This map shows the number of jobs located in census blocks near transit in the Atlanta region. Click any block to see the number of jobs located there.
The US Census provides us with the number of people who live in each census block and the number of jobs located there. We can use the Origin Destination Cost Matrix Network Analyst tool to calculate the travel time between sets of points.
This analysis is about to get complicated, so we'll work our way up by way of another simple example (next).
Do you have access?
Let’s calculate the travel time from just one census block in Atlanta (the red block in the map) to all other census blocks. We can determine which other blocks are reachable within a 30-minute travel time (the ones with the white outlines).
As we know, the available transit service differs based on time of day. If our commuter leaves at different times, a different set of blocks may be reachable. Use the vertical swipe bar in the map to compare the reachable blocks at 6:30 AM (left) and 8:30 AM (right).
We can sum the number of jobs located in the reachable blocks. Someone living in the highlighted census block could reach 151,487 jobs within 30 minutes if they left the house at 6:30 AM. But for an 8:30 start time, they have access to only 105,187 jobs within 30 minutes
You can create a map like this using an Origin-Destination Cost Matrix analysis and a transit-enabled network dataset created in ArcGIS Pro. The census block polygons' centroids were used in the calculation, which effectively assumes that the entire block area, population, and jobs are concentrated in that one point. This is a reasonable assumption for smaller blocks, although for geographically larger ones, it may not be terribly accurate. Smaller geographic divisions are generally better for pedestrian-scale analysis, but demographic and employment data is typically not available for divisions smaller than census blocks.
How often do you have access?
Suppose we run the previous analysis for each start time between 6:30 and 9:30 AM. We can calculate that the 11 people who live in our origin block have at least one opportunity to access to 204,381 jobs (jobs reachable within 30 minutes for at least one start time). However, if we consider only the blocks that are reachable frequently (reached within the 30-minute travel time limit for more than 90% of possible start times), we see that the number of frequently accessible jobs is only 67,680.
Now suppose we run this same calculation for all census blocks within the city limits of Atlanta. The maps here show the number of jobs accessible to each census block within a 30-minute travel time at least once within the time window (left side) and at least 90% of start times within the time window (right side).
The point is that because the available transit service changes throughout the day, some jobs are easier or more convenient to reach than others because you have more opportunities to reach them. For some jobs, if you miss your bus, you can just catch the next one and still be at work on time. For others, if you miss your bus, you might not be able to get to work at all. Access to opportunities by transit may be intermittent.
You can make maps like this using the Calculate Accessibility Matrix tool, part of the downloadable Transit Network Analysis Tools tool suite.
Do you need more access?
Not all blocks need access to jobs. Some blocks have no population. If we’re concerned about job accessibility in our city, we probably want to identify areas of the city which have both a high population and also poor access to jobs.
The ratio of population to number of jobs accessible within 30 minutes is informative and is shown in the map here (higher ratio, brighter orange). Click a block to see the ratio of population to number of jobs reachable within 30 minutes.
Most census blocks within the Atlanta city limits seem to have a pretty healthy ratio of population to job opportunities, but there are a few blocks that stick out and probably warrant some further investigation. Possibly we don’t expect people to commute to jobs by transit in the suburban areas, but we might be able to use this map to identify a few areas of town where we want to extend transit lines, increase frequency of service, provide better pedestrian infrastructure, or even pursue some transit-oriented development.
Of course, with all the above said, what really matters to someone is not the sheer number of jobs accessible but whether or not they have access to their job. This analysis does not give us that information. Nevertheless, the number of jobs accessible tells us something about the level of opportunity available to residents of different neighborhoods and could highlight disparities between neighborhoods. Depending on our goals, we could further refine this analysis by breaking down the jobs into job type categories or incorporating other demographic data.
Wrap-up & Resources
Public transit analysis is a complex and nuanced subject with lots of opportunity for interesting GIS analysis.
Want to learn how to do analyses like those shown in this Story Map? Check out our comprehensive tutorial video series .
Some tools, example analyses, and other resources are available on the website shown below.
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We hope this Story Map has been helpful and inspiring to you. Feel free to send us your feedback, and we would love to see the results of your analysis! Please reach out to your Esri representative or post in the Esri Community forums .