What is the shape of the barrier in the TV series Under the Dome? Is it indeed a dome shape, or does it encircle the entire town like a spherical bubble, with one hemisphere above ground and the other hemisphere underground?
Inside a sphere.
In one episode (second or third, IIRC) two of the characters (Junior and Julia, the reporter) went into some old tunnels under the city to see whether they could go under it. They ran into the dome down there as well and so concluded it was indeed an all-encompassing sphere.
In later episodes, we see a mini-dome that apparently houses the source of the large dome. The mini-dome is in fact a sphere, suggesting that the larger dome is likely to be a sphere as well.
I'm going to disagree with the accepted answer.
If the TV series follows the book, it's most likely an actual dome. It's just that the dome goes very deep.
How do we know it's a dome and not a sphere? Well, in the book's ending:
Julia convinces the "leatherhead" alien girl to lift the dome, which it does quite literally: it lifts the generator and with it goes the dome, upwards. Private Ames, who is helping Ollie at the time, feels the edge of the dome as it goes upwards, scraping his back. Had the dome been a sphere, there would have been no way for it to go upwards without taking the whole town with it.
Of course, I'm assuming the TV series will have the same ending as the book.
EDIT: I just read that Stephen King is on record saying the TV writers changed the source of the dome, so all bets are off for the TV series.
At first we were led to believe it was a dome but in recent episodes
we see the "generator" of the dome in Joe's garage, and it is a sphere shape, thus leading us to believe they are in a sphere.
The series should be called “IN THE SPHERE”
The dome is actually a spherical bubble that encompasses the whole town. This is why they can not find the edge of the dome trying to dig under it to escape. The sphere is actually a force field that prevents anyone from penetrating it. This sphere was sent from outer space by an alien life form to bring the town back to their planet for research into how people on earth live. It’s like a Guinea Pig in a glass sphere. Eventually the town will be lifted off the earth and hurled into space for its long trip to the alien planet. The people in the town are already experiencing the effects of the alien’s experiments by them seeing loved ones that have passed away years ago. Will this place in space be Heaven? We will just have to wait and see.