The tiling boundary is shown on the left and right sides of the screenshot, the elbow pipe. It should be connected to a source of crude. This wall is a derivative of my favorite wall design so far (credit to JinM), but with some changes and additions of my own.
I have added an emergency power source to power the gun ammo inserters in the event of a power emergency on the main grid, and a dedicated crude storage tank to feed the flamethrower turrets in case the crude source dries up; the pump acts as a motivator and a valve, even in a power emergency. The roboport is not connected to emergency power, but should be supplied with repair packs externally. The requester chest requests both piercing ammo and regular ammo, in case one or the other runs out, with piercing taking priority. I've also added some landmines out front for extra protection, and stylish concrete for flair.
As with the wall this version is based on, the spacing is ideal (as long as you tile using the screenshot as a guide; edge of the picture is the edge of the tile) and provides full wall coverage as both biters and spitters will naturally gravitate toward the turrets. Overlapping laser, gun and flamethrower turrets will make short work of anything, especially if you have damage research far along.