I was asked that during my commercial checkride. I didn't know the answer so the DE told me but my mind was in such a fog by the end of the test that I don't remember the answer.
He pointed at the houston class b and asked me what the geographical center was - I told him it was the largest airport in the area. Then he wanted to know which part of the airport was the center - was it the approach end of the runway, the geographical center of the airport, or what?
Then he pointed to the veil around class b and noted that it was offset and asked what the center of the veil was - I didn't know so he told me. But now I'm trying to write up my notes and I can't remember the answer.
Anyway, that's the point of the question...I'm just trying to organize things in case I get asked the same questions again on another checkride.
FAR 71.41 "Each Class B airspace area designated for an airport in subpart B of FAA Order 7400.9M contains at least one primary airport around which the airspace is designated."
FAR 91.215(B)(2)"In all airspace within 30 nautical miles of an airport listed in Appendix D, Section 1, of this part from the surface upward to 10,000 feet MSL."
Don't worry about his specific questions. He is/was digging for trivia which has no practical purpose except to rattle you.
The rings around a class B airport are from the "geographical center", whatever that is. Many class B areas have more than one primary airport so there are multiple "centers." The 30nm Mode C veil was started when TCAs became class B and Mode C transponders weren't required for just about everyone. Now that many Class B areas have grown so much, the Mode C veil is actually INSIDE the outer Class B lateral areas. I find that amusing.
Anyway, the 30nm veil is centered around AN airport. You have to look at the chart to find it. I think it's hobby in Houston.