A reader asked where they could get Chicago Transit Authority (CTA) data I didn’t already have on the “Find GIS data” page. I only had shapefiles for train lines and stations. Now I’ve got bus routes and stops.
You can download General Transit Feed Specification (GTFS) data from the CTA’s Developer Center. It’s updated regularly when service changes.
Screenshot from ESRI ArcMap showing the unedited shapes.txt file loaded via Tools>Add XY Data. Shapes.txt is an 18 MB comma-delimited text file with thousands of points that can be grouped together with their shape_id.
The GTFS has major benefits over providing shapefiles to the public.
- It can be easily converted to the common shapefile format, or KML format.
- Google, the inventor of GTFS, has defined and documented it well; it is unencoded and plaintext. These attributes make it easy for programmers and hackers to manipulate it in many ways. (see also item 4)
- Google provides a service to the public on its website, an easy to use and robust transit planning service.
- The data is stored as plaintext CSV files.
- While an agency like CTA may have a geodata server on its intranet, it is less likely it has the addons that provide mapping and geodata services for the internet. A server like Web Mapping Service, or ArcIMS. These systems can be expensive to purchase and license. And we all know how the CTA seems to always be in a money crunch. While the CTA updates its GTFS data for publishing to Google Maps, the public can download it simultaneously to always have up-to-date information, providing the same geodata that ArcIMS or WMS would offer but for no additional cost.
I couldn’t have pulled off this conversion in 24 hours without the help of Steven Romalewski’s blog, Spatiality. He pointed me to the right ArcMap plugin in this post about converting the Metropolitan Transportation Authority’s GTFS data into shapefiles. I hope Steven doesn’t move to Chicago less my authority on GIS and transit be placed in check!
Make your own map of the CTA train routes and perform some kind of analysis – then share it with the rest of us!
Read more about my exercise in geodata conversion in the full post.
I had tried converting the information using the free and open-source QGIS software. I might try again, or perhaps use uDig, GRASS, or Cartographica. My trouble started when I tried to use fTools to join two tables (er, CSV files). After failing with QGIS I tried to join the tables using PostGIS (on a local PostgreSQL server). I was able to successfully join the tables and then use QGIS to connect to the PostgreSQL server to load them into the map. I ran into some problems with this (maybe I was just impatient), but I tried again after trying the ArcGIS method of joining (easy) and converting (plugin required) and pulled the data into the map. The next problem to solve is converting these points to polylines.
If you’re an open data advocate looking for an argument in which to take part, I recommend the discussion on Streetfilms: A Case for Open Data in Transit.