It's a relatively old sport with terminology going back a ways, but still very useful.

"Gear inches' is actually the diameter in inches of the drive wheel of a penny-farthing bicycle with equivalent gearing."

Read this:
https://en.wikipedia.org/wiki/Gear_inches

For comparison purposes, the whole point of GI, your set-up produces a 70.9 GI while my 48x18 700x25 is a 70.3 GI .
Two "different" ways to get very traditional and useful fixed gearing for riding on the open public roads., although per @JohnDThompson I'll stick with my well proven lighter set-up over yours.

-Bandera