The rankings are divided between universities that have Ph.D. programs and universities that don't. Our school does not officially have a Ph.D. program and therefore is ranked with those that do not. This group of universities that only go up to Master's programs are ranked according to regions, and our school is #2 in the West. Our school of engineering was also ranked #14 nationally last year.
The tiers just refer to a number of schools that are tied and thus are listed together as a tier, but has nothing to do with highest degree of education.