Raised pattern on casting surfaces

[CRS]

Can anyone shed some light on why some blocks and head castings have a small raised pattern across the surface?

casting surface.png

Is it to increase surface area or something else entirely?

Thanks

[ZEOHSIX]

Adds strength to reduce cracking.

[swampbuggy]

X 2

[Kevin Johnson]

Besides the above it can change the acoustic properties and help to reject heat from the casting. Rover used this type of surface in a cast pan to help the surface capture oil droplets shed from the rotating assembly (BMW too -- I think they shared that tech with Rover). Seems like Porsche used it as well in this manner on the interior of some crankcases. Sometimes you can see it on the underside of pistons for above reasons.

[pcnsd]

Looks like it was conceived to spread stresses.