A quick way of deciding if you're being ripped off for data roaming fees

A lighthearted thought experiment:

.... visit a city in a new country. Plan a journey from your hotel to a typical "point of interest" perhaps a mile (1.6km) distant.

Is it cheaper to:

(a) Walk, using Google Maps or a similar mapping product on your phone, consuming roaming data to show you the city's layout and plot a route as you stroll across town.
(b) Jump in a taxi. the driver worry about the route instead, and pay based on the meter

If the cost of the data roaming > cost of a local taxi, I think you can be fairly confident that you're paying your operator too much. Or else you're somewhere with really cheap taxis.