I like to use the insurance companies view when they underwrite homeowner's insurance. Seems like they have a good grasp on the terms.
Having public utilities and police/fire protection COULD be classified as urban. If it smells like the city, it probably is.
Suburban COULD be classified as having some public utilities and some police/fire protection. Generally, having public water/no sewer or visa versa, with 3+ visible neighbors and a volunteer fire station would/could be suburban.
Rural, having no public utilites and fire protection farther than 5 miles and no local police protection, usually covered by State patrol. Fire protection supplied by tanker trucks due to no public water supply. No visible neighbors.
With that said, I personally live on 80 acres, private well/septic, no visible neighbors and live less than 1 mile to a town that offers public utilities, police and services. My insurance company defines me as urban (protection class 3 on a scale of 1-10)......go figure...
This is by no means GOSPEL. It is my opinion only and this topic has been debated since I first joined here. It is merely an opinion and given so you may incorperate it into your ideas of what is rural or not. Better yet, why not search for your answer. You will find at least 100 seperate answers on this subject. You know what, just forget everything I said. Without 20 years of experience under my belt, I really have no clue to what you asked about...