The Federal army, under Schofield, had the huge advantage of Ft. Granger, which sat just south of the Harpeth River, and east of Columbia Pike.
The picture below (click on to enlarge) shows the view from Granger. From the yellow pin designating Ft. Granger one can see Carnton at 12 o’clock (about a mile away), the Carter House at 2 o’clock (about a half mile away), and Winstead Hill at 1 o’clock (about 2 1/2 miles away.
Granger had several large guns in position during the Battle of Franklin. Loring’s and Wathall’s Divisions came from the southwest, crossing Carnton plantation. These Granger guns decimated these divisions from nearly a mile away.
The next map (click to enlarge) shows the Confederate Army of Tennessee as it approached the Federal lines at Franklin. Notice how the Federal position leveraged several geographic features. (1) Using the Harpeth River and the Nashville-Decatur Railroad as a natural barrier for their far left flank. (2) Position of Ft. Granger to protect that left flank. (3) The osage orange abatis also protected the far left flank, making it nearly impossible to penetrate.
Here’s a schematic of the design and layout of Fort Granger.