The General Transit Feed Specification (GTFS) defines a common format for public transportation schedules and associated geographic information.

source

It contains data about several data concepts, with the general idea that this data is relevant for the end-user and planning tools. Look at the reference for more details.

Concept	Remark
General information	Agency (stop_)areas translations feed info
Routes, trips	Routes trips frequencies transfers
Fares	rules products attributes
Calendar	calendar dates
Pathways, levels	pathways levels shapes

No modifications are known in the scope of city-TO relation, but all GTFS files don't contain (in)direct personal data.

The fields in the JSON are described here, but only those that need explanation. The values in the building block, are fixed, unless they are between square brackets ([]).

name	required	value	description
version	*	[1.1 < version < 2.1]	The allowed version(s), comma separated. Replace this value by f.x. "1.2,2.0,2.1"
url	*	[url]	The URL where this file (or endpoint) can be found, f.x. "https://example.transporter.com/gtfs/agency.txt"
refreshRate		[refresh rate]	The refresh frequency. Specified in 8601 Duration (see https://en.wikipedia.org/wiki/ISO_8601#Durations). f.x. "PT5M" for 5 minutes.

name	value	argumentation
privacy	A	No data set is conflicting with GDPR or related to persons
implementationEffort	B	When it is implemented as separate files, it is the simplest implementation, an A.
reusability	A	This data can be applied in several domains, to exchange between TO and MPs, towards route planners, and to cities.
interoperability	A	This is a worldwide standard (A).
domain	B	When applied in the domain city-transport operator, it would be an A, but this standard is made to exchange data in the mobility domain. Not a perfect fit.