Those lines are texture seams, people - jesus.
The texture used to cover the map started off huge - like 1024x1024 or such, then split into multiple 256x256 textures. The texture coordinate assignments in Hammer Editer pretty much suck, therefore you get a small seam where the edges of the differant textures come together.
Also - SLASH - the image you posted is very offensive and inappropriete - please find another way to entertain yourself.