Just finished reading this book.
The title is a bit misleading in that it implies, to me at least, that the author feels that the battle location was inevitable given that Gettysburg was a major road junction. Harman does show that when the ANV moved into the Susquehanna valley and the AOP into the area north and west of Washington and Baltimore that Gettysburg became one of three or four locations where they would do battle. The confluence of roads, the existence of railroads and significant sources of water determined this. He posited that a Civil War army could not remain in one place for more than 24 hours without road and/or rail access and a sufficient water source.
However, more of the book is about how the AOP positioned itself to take advantage of the environment, as Harman terms it and to protect access and water supply.
In addition there were a couple of things that were new to me. The first was Meade's plan to initiate an attack on his right using the 12th and 5th Corps, with the 6th Corps in reserve, provided it arrived in time. This option was not feasible once Slocum pulled those two corps back without consulting Meade.
The second was the sighing of McLaws division on its backtrack route north, by the signal station on Round Top. Meade mistakenly interpreted this as a possible move on his right flank, which led him to consider an assault there more likely than on his left.
There were roads from the Emmitsburg Road to the Taneytown Road south of the Round Tops, that could have been used by Longstreet for a tactical movement around the AOP left flank. Meade moved to protect this on July 3 by moving Merritt and Farnsworth into the area and by providing 6th Corps support. The point is that Longstreet's argument for a move around the Union left had more merit than I had believed.
Overall a good book and worth reading. It does require at least a basic understanding of the Battle of Gettysburg, though.