Which special interest is closest to state capitols?

Education school Jay Greene launched a new blog on education policy with post on the proximity of teacher unions to state capitols.

If you stand on the steps of a state capitol building and throw a rock (with a really strong arm), the first building you can hit has a good chance of being the headquarters of the state teacher union. ...

Of the 25 most influential interest groups, the teacher union is the closest in 14 of the 50 states. The labor union, AFL-CIO, is the closest in 7 states. The American Association of Retired Persons (AARP) and Nation Federation of Independent Business are the closest in 5 states, each. The trial lawyers lobby, the American Association for Justice, is the closest in 4
states. ...

In Nebraska, the teacher union office is only 210 feet from the capitol building. In Pennsylvania it is only 312 feet away. In Alabama, Delaware, and South Dakota, the teacher union headquarters is about 500 feet away. ...

The teacher union doesn’t strive to be the closest because the extra time it takes to walk or drive a few more blocks will make the difference in a pivotal vote. They strive to be the closest because it is a visible display of their power and influence.

In fact, not only is the PSEA building a stone's throw away from the Pennsylvania Capitol (and an easy target, even for the weak-armed, as it is among the tallest buildings in Harrisburg), but so is the "Historical Marker" for Public Sector Unionism in front the PSEA headquarters, another display of their power and influence.