Tourists, Vacationers, Travelers, and Visitors

What is the difference between tourists, vacationers, travelers, and visitors? There does seem to be a negative connotation attached to "tourist" that may not be a part of our understanding of the other terms. If I travel to a new place, does that automatically make me a tourist or is being a tourist a way of visiting a place? Does length of stay matter? If so, how long do you have to go in order to stop being a tourist? Is vacationer more or less shallow than tourist?