It's both. They do group interviews in a different cities, you can always wait until they come to a town near you if you're not in a hurry (the schedule is on the website). You don't need an invite, you can just show up.

The group interview is part presentation and part interview. They will talk to you maybe briefly, maybe at length and may do full HR and technical interviews and written tests. You will likely be invited to complete the interview in SLC, probably sooner rather than later.

Wear a suit and be 100% prepared for an interview (they will not do the sim until you go to SLC however).