Not a question but rather a random observation:

https://www.pottermore.com/writing-by-jk-rowling/professor-mcgonagall

I read this ages ago; not sure why it didn't stick in my mind.

So the existence of multiple teachers per subject is now canon, opening the door to a larger Hogwarts population.

The tricky part of this is of course the DADA position, since there only being one teacher of that subject is a plot point -- both in terms of the curse on the position, but also in terms of Dumbledore not being able to find a single person willing to teach the subject in OotP, resulting in Umbridge's appointment.

I think we will just have to say that DADA is the only subject with just one teacher, perhaps because of the curse.

 

That, or it's simply an oversight. With JKR, that's more often the answer than not. After all, in Book 2, Riddle refers to Dumbledore as the Transfiguration teacher, which seems to imply that there's only him.

 

My headcanon is that at one point in time, there was a need for extra teachers. I mean, even if you do the math with current supposed Hogwarts students, you would need multiple ones to get a reasonable schedule to actually work. But, I like the common fanon assumptions that there are tons of extra disused classrooms, and with two major wars in the last 100 years, the wizarding population is at a very low point, so there's not as many students as in times past. But, I think the true answer is the same as it's always been, and that JKR is not good with numbers, and anything mentions as such outside of the books is retconning/backtracking, which isn't necessarily bad when it comes to numbers.

 

Personally I've never been a fan of the idea of the wizarding population being in decline due to wars -- I feel like it fundamentally misunderstands the type of war that magical people engage in. This isn't a WW1/WW2 style "total war". There are no armies clashing. Death tolls are more like those of a very successful serial killer than a war.

Also, I'm not sure that there's much evidence in canon of empty classrooms. For example, in GoF, Harry and Hermione ask McGonagall if they can use her classroom to use to practice the Summoning Charm. That wouldn't have been necessary if there are lots of empty classrooms.

 

The sequence took place in the 1910s, a few decades before Voldemort started school, so Dumbledore might've started out his teaching career as a Defence teacher, and switched to Transfiguration.

 

Doesn't she only do that because she was 'tired of encountering Harry and Hermione in abandoned classrooms'? Or something like that.

 

I'd assume it was though, since Harry's year, and the few years before that were mostly born during the height of crisis. I don't think most people would have been willing to have children during a time when it was not an exaggeration to think that they could be murdered the next day.

I think the years following Ginny's year would have significantly more people, considering that there would most likely have been a baby boom after the fall of Voldemort.

 

Personally I think that the issue with population is due to Rowling not putting much thought into the numbers. Rowling herself said that she imagined Hogwarts having about 1,000 students. I know that the books take precedence over author statements but in this case I'm willing to take it. The descriptions of the Hogwarts halls between classes and the Great Hall during mealtimes seems awfully crowded for a population of about 280 students and unless just about every wizard in Britain works at the Ministry then Harry's description of hundreds of wizards in the Atrium of the Ministry of Magic doesn't make much sense.

 

Does Canon say anything about how fast/far owls are able to travel?

 

I'm a few posts late, but as far as the empty classrooms thing goes, go take a look at any school. Not all classrooms are in use all the time.

The only mention I can recall of a disused classroom is the ground floor room off the entrance hall which Professor Pony Firenze moves into.

 

A concept I have always liked (but seldom seen implemented well) was Hogwarts adjusting to its students‘ needs, which would include castle size. For example, we have the Room of Hidden Things, where it is not entirely clear where or how it actually exists – I would assume expansion charms are at work, but that still leaves the issue of where it actually, physically is. As such, I would imagine extra classrooms popping in and out of existence as the size of the student body varies would not be entirely impossible to fathom as far as canon magic is concerned. That would also lend a bit more importance to the moving staircases, which could function as access points when needed.

 

Fun thing about an adjustable castle- it'll have just as many rooms as it or the headmaster believes is needed.

Here's an interesting reference:

This suggests that there are as many as 27 windows along one floor between a tower and the other side of that structure; otherwise, the headmaster would suggest they count from the other side.

 

I've always assumed that, at least for classes, the residents of the castle stuck to the areas that were mostly constant, and easy to use. No walls pretending to be doors, or doors pretending to be walls... Or doors that are only there if you aren't looking, or it's a Wednesday.

Technically, you can work in the left hand corridor of the third floor, but you can't go back the way you came, and current estimates put it at five miles long. As such, nobody really likes having classes there. Professor Firenze does enjoy taking an afternoon constitutional along the way, although he'd much rather it wasn't cobblestone.

And nobody uses the North half of the fifth floor, because ever since Phlogistious Black did some 'experimental alchemy' in the 1700's, it's quite impossible to breath there, without the assistance of a bubble-head charm.

 

In CoS, when Harry is "caught" by Peeves during the second petrification, the scene suggests multiple classes are taking place along a single (nor particularly long) corridor.

It may well be that the excess space serves some function beyond "disused classrooms", and Harry is simply not privy to it. But I think it is reasonable canon conjecture to assume that the students actively utilise a small portion of the castle, personally.