In a medium saucepan, over high heat, boil the cider until it has reduced by half to 1 cup, about 20 minutes. Cool over an ice bath until at room temperature.
Combine the cider, bourbon, lemon juice, maple syrup in a medium bowl. Divide among 4 8-ounce glasses, add a few ice cubes, and top each glass with a splash of seltzer. Garnish with ginger slices. Serve immediately.