The y-axis is how much of an insider or outsider the candidate is; the x-axis is how moderate to conservative the candidate is. The size of the circle is how currently popular or powerful the candidate is. The color of the circles represents the region the candidate hails from: Northeast is blue; South is red; Midwest is green; and West is yellow.
The GOP leaders who most interest me aren't on the graph: Chris Christie and Paul Ryan. Of those who are on the list, the candidates who most interest me on the right side of the graph are John Bolton and Rick Santorum, for their foreign policy and social issues (pro-life) bona fides, respectively. I don't believe either can win -- as the smallness of their circles suggests -- although I do think Santorum, had he not lost in 2006 in a horrible year for Republicans, would have been an obvious candidate for 2012 (he would have been 18 years into a distinguished Senate career from a key state, Pennsylvania). Instead, I fear that the two big circles in the upper left and lower right quadrants will suck all of the juice out of the race, and we'll have a Romney v. Palin match -- Eastern establishment moderate versus Western outsider conservative -- in which Romney will be the inevitable winner as the supposedly more "electable" alternative. But Romney is severely flawed due to the Massachusetts version of Obamacare he signed off on; he's Mormon (shouldn't matter, but it will); and he's distrusted as a flip-flopper by the social issues wing of the party (Evangelicals and Catholics).
Is this why there have been what can only be understood as trial balloons floated recently in National Review (here and here) about reviving the political career of Jeb Bush, the former governor of Florida and, of course, the son of you-know-who and the brother of you-know-who-II?
Hot Air also has an article up about Rick Perry, the Texas Governor, who is "oddly" focusing on what might be seen as hot-button national issues such as border security, abortion, eminent domain, balancing the state budget, and voter ID. If Jeb Bush and/or Rick Perry got into the race, there would be some excitement.