On-campus interviews are the less common type because schools try to accommodate their applicants the best they can. On-campus interviews are more likely for an interview conducted by an admissions officer, and very likely if there is more than one admissions officer who will be interviewing you. If you get the opportunity to go, you should try very hard to take it. If the school you are applying to is too far for you to travel to, it is acceptable to tell them that. Sometimes they have a financial aid budget for traveling. If you cannot make it, you should ask if you could do it over the Internet or phone.
The second type of interview is off-campus and is very popular. These interviews will most likely take place near your hometown and will be in an informal setting, such as a coffee shop, or a formal setting, such as the business office of the interviewer. You should match your attire based on the location of these interviews. Unlike the on-campus one, some venues allow you to dress business casual rather than business professional. For example, if you are meeting at a coffee shop, it is fine to ditch your sports coat or your best high heels.