Hey Moshe,
From LSAC: "A national school will generally have an applicant population and a student body that draws almost indistinguishably from the nation as a whole and will have many international students as well. A regional school is likely to have a population that is primarily from the geographic region of its location, though many regional schools have students from all over the country; a number of regional schools draw heavily from a particular geographical area, yet graduates may find jobs all over the country. Generally speaking, a local school is drawing primarily on applicants who either come from or want to practice in the proximate area in which the school is located."
Here's more info on that from our Admissions Free Help Area:
http://www.powerscore.com/lsat/law-scho ... _faq.cfm#8
To answer your second question: No, all T50 schools are not national. In fact, the majority of them are not, although some have wider alumni networks that could make them more "national" than others. There's no list out there that you could consult since, once you get out of the T14 (where one could argue that all schools could boast the "national" title, given their brand recognition and general prestige), whether a school is slightly more national than regional is a subjective thing that will change based on the reach of the alumni network and where students are able to get jobs. I would say that, as a general rule, any state schools are regional. To figure out if a school is national or regional, take a look at three things:
1. Where students hail from in an incoming class. The bigger the number of states and countries, the more national the school.
2. Where alumni are located. Again, the bigger the number of states and countries, the more national the school.
3. Where students get jobs. Ditto to the above.
Keep in mind that percentages rule. So, for example, if a school has most of its students, alumni, and jobs in the state they're in and the surrounding ones, then they're regional, even if they have a few students on the opposite coast and a sprinkling of alumni internationally.
Hope that helps!