Preparing a baseline transport network

Accessibility calculations will be based on transport networks that is set up in your region. Transport networks includes scheduled transit service as well as the region’s streets, sidewalks, bikeways, etc. Initially you will set up a baseline network. Later on you will likely want to compare alternative scenarios by creating modifications to the baseline network.

Setting up a new region

The region is a bounding box defining the area to be used for accessibility calculations. It should generally cover the entire service area of the agency or agencies you will be working with. Opportunities and network components outside this area will generally not be considered.

The regions page, shown after you log in, provides a list of existing regions (if any), and the option to create a new region. It is also accessible at any later point by clicking the globe icon (). From the regions page, set up a new region by clicking:

Set up a new region

Start by using the search bar in the map to automatically locate your city or country by name. You can also move the bounding box by dragging its corners on the map or by manually entering coordinates in the sidebar.

Enter a name for the region and an optional description. To finalize region creation, click the button at the bottom of the panel. You should then be prompted to create a network bundle.

Creating a network bundle

Conveyal Analysis requires a network bundle, which consists of street and transit data.

To create a network bundle, click on the Network Bundles icon (), then click:

Create a new network bundle

In the panel to create a new network bundle, first enter a name. We recommend staying organized by basing the name on the time period and/or services included, such as “April 2020 - Transit and Commuter Rail Feeds.”

You can then specify whether your new bundle’s street data (OSM) and transit data (GTFS) should be re-used from existing data, or based on new data that you upload.

Preparing the OSM data

OpenStreetMap (OSM) extracts define the street layer of the baseline transport network. This layer will be used for any walking or biking segments of a trip as well as for some transfers between stops and stations.

If you or your team has previously created network bundles in this region, you can select any one of them to re-use its OSM for your new bundle.

If there are no previously created network bundles, or if you want to use updated OSM data, you will need to upload a new OSM file. Note that while several formats exist for OSM data, Conveyal requires uploads in the PBF format because it is more compact and faster to process. The following sub-sections include detailed suggestions on preparing OSM PBF data for upload.

Downloading

Extracts from the global OSM database can be downloaded in many different ways. Some popular services like those provided by Geofabrik or Nextzen provide easy downloads for selected cities and regions. Be sure to download data covering your entire region - the predefined areas used by these sites may or may not align well with your region. Your extract should cover your entire service area or region, but not extend unnecessarily far beyond it as that may impact processing time. You’ll often need to download an extract for a country or region larger than your true analysis area, then crop it to the size you need.

Cropping

Performing accessibility analysis with excessively large OSM data can lead to significant increases in computation time and complexity. We strongly recommend cropping the data if they cover an area significantly larger than your transportation network or opportunity data. Several command line tools are able to perform these cropping operations:

  • Osmosis is a multi-platform Java tool that works on Windows, Linux, and MacOS.
  • OSMConvert is a fast tool pre-built for Windows and Linux and available on MacOS and Linux as part of the osmctools package.
  • Osmium-Tool is a personal favorite that is extremely fast but only straightforward to install on Linux and MacOS platforms.

Below are some example crop commands for these different tools. You’ll need to replace input.osm.pbf with the name of your downloaded PBF file and change the coordinates of the area to clip to.

When uploading new OSM, the network bundle creation panel will show osmconvert and osmosis commands pre-filled with the current regional bouding box. If you have either of these tools installed locally, you can paste this command into to your local command line and modify the filenames to crop your OSM data to regional boundaries before upload.

Osmosis:

osmosis --read-pbf input.osm.pbf \
  --bounding-box left=-79.63 bottom=43.61 right=-79.12 top=43.83 \
  --write-pbf cropped.osm.pbf

OsmConvert:

osmconvert input.osm.pbf \
  -b=-79.63,43.61,-79.12,43.83 --complete-ways -o=cropped.osm.pbf

Osmium-Tool:

osmium extract \
  --strategy complete_ways --bbox -79.63,43.61,-79.12,43.83 \
  input.osm.pbf -o cropped.osm.pbf

The latter two commands expect bounding boxes to be specified in the format min_lon,min_lat,max_lon,max_lat. We frequently find bounding boxes using the convenient Klokantech bounding box tool. Selecting the “CSV” format in the lower left will give exactly the format expected by these tools. You can also adapt the bounding box values shown in the region setup panel of Analysis.

Note that files larger than 500MB may be rejected on upload. Please contact your support team if you genuinely need to upload a file of this size, or need assistance in cropping and filtering OSM data.

Filtering

OpenStreetMap contains a lot of data besides the streets, paths, and platforms we need for accessibility analysis. As of this writing more than half of the ways in OSM are buildings, and slightly less than a quarter are roads or paths. Filtering out unneeded data will reduce your file size and speed the upload and processing by Analysis. As in the previous section, sample commands are provided below that will remove any unneccessary tags and should dramatically reduce the output file size.

Osmosis:

osmosis \
  --read-pbf input.osm.pbf \
  --tf accept-ways highway=* public_transport=platform railway=platform park_ride=* \
  --tf accept-relations type=restriction \
  --used-node \
  --write-pbf filtered.osm.pbf

Osmium-Tool:

osmium tags-filter input.osm.pbf \
  w/highway w/public_transport=platform w/railway=platform w/park_ride r/type=restriction \
  -o filtered.osm.pbf

Uploading GTFS feeds

If your new network bundle will not be re-using previously uploaded GTFS, start by gathering GTFS feeds for the transit agencies whose service you want to include. A GTFS feed is a set of CSV files inside a .zip archive.

Once these files are gathered on your computer, select the .zip files to upload in the “Upload new GTFS” tab of the network bundle creation panel. You can select multiple GTFS feeds in the file dialogue by shift-clicking, control-clicking or command-clicking (depending on your browser/operating system).

Again, note that files larger than 500MB may be rejected on upload. The largest GTFS feeds in regular use are below 400MB and most are much smaller than this. A larger file may indicate a problem. Please contact your support team if you genuinely need to upload a larger file.

If there is no GTFS available for your region you can, as a workaround, create a blank slate by using a valid GTFS feed from somewhere else in the world. After creating a project as described below, you can then attempt to import modifications from a shapefile representing service in your region.

Ensure any GTFS you upload follows requirements of the specification. Various validation tools are available. Common issues include:

  • Missing required files
  • Calendar dates that do not cover an intended date of analysis.
  • Using values other than 0-7 in the route_type column of routes.txt

Conveyal’s routing engine currently treats all GTFS trips represented in frequencies.txt as unscheduled frequencies (exact-times = 0). If any of your feeds has a frequencies.txt file with values of 1 in the exact-times column and you’d like to learn more, please contact your support team.

Finalizing network bundle creation

After you have specified a name for the network bundle, OSM data to re-use or upload, and GTFS feeds to re-use or, click the create button to confirm. You will need to wait a few minutes for Conveyal to process these data.

Creating a Project

Uploading and processing a network bundle may take several minutes. Once processing is complete, you should be able to create a new project based on the bundle you uploaded. If you aren’t on the projects page already, click the project icon () and then,

Create new Project

A project is essentially a wrapper around a bundle which associates it with any scenarios and modifications you may create later on. The purpose of projects is to allow multiple users to work simultaneously on the same baseline network without stepping on each other’s toes. The section on Managing modifications describes how modifications can be shared between projects that are based on the same bundle. Once created, the bundle associated with a project cannot be changed.

Give the project a descriptive name, select a bundle to which the project will be associated, and click the create button to confirm. You are now ready to move on to editing scenarios.