The comparison between where I can smoke a conventional cigarette vs. an electronic cigarette, is well marked and differentiated. For example, a normal cigarette can only be smoked outdoors and in some areas such as private areas, neither in meeting rooms nor in public places, cinemas, theaters, etc.
Contrary to electronic cigarettes, they have more amplitude on their use, even in closed spaces. The only exception known so far is in public organizations where it is prohibited. vapingThe only exception known so far is in public agencies where vaping is prohibited, meaning agencies attached to national or state governments, whether they are schools, post offices, city halls, etc.
Everything will depend on the restriction of each place.
In places such as airplanes, shopping malls, restaurants, private offices, etc., in these places the only restriction would be from the owner or managers of any of these places who could establish rules in their establishment.
We have for example some restaurants where the owner allows the diners to vape. On the other hand, there are others where the rules are different not allowing vaping by decision of its owner, another case we can mention is the fast food chain McDonald's, where they do allow their visitors to vape electronic cigarettes, but in Starbucks Coffee (in the closed area) is totally and absolutely forbidden.
There is also the case of airlines; depending on their policies, some of them allow vaping without any problem in their airplanes and others do not. In the case of public transport belonging to the state this will depend, but most of the time it is forbidden to vape, in some offices you can do it as long as the employer consents, otherwise you can not do it either.
This regulation has a background, which is to avoid that the worker has the need to go out to vape or smoke a normal cigarette, which would interrupt their work and therefore cause loss of time.