Traveling around Europe I grew to rely more and more on Google Maps (GMaps) public transport data. That is if I am in a new city and need to get from A to B, GMaps is normally very effective in generating a good route by bus/train/metro/tram.
Recently though we've been in Toulouse, where this is hardly the case. On multiple occasions GMaps had very limited or no information, and we were able to find much better options elsewhere (asking people around, local websites, etc). Not only us, it seems. Example: GMaps had literally no options for going from city center to the airport, even though it was very straightforward, few stops by metro and then tram.
That's fine, one cannot expect to have perfect coverage for such variably-sourced data everywhere. But I am having hard time figuring out how to prepare for that. So the question here is: knowing your destination city ahead of time, how to best figure out if GMaps has sufficient data for the area (and research alternative local apps/maps if it does not)? Or perhaps the whole premise is wrong, and one should never rely on just GMaps?