What I understand mathematically: The Polyakov action has three symmetries of the world sheet(reparametrization-inv.,Weyl inv.). These can be used to take the worldsheet metric into the form diag(1,-1), i. e. it is a flat space. But I don't understand that when I try to visualize the worldsheet of a string oszillating in some (spacelike) direction because the corresponding worldsheet is not flat then anymore. There are these bulgs in the oszillating direction which make the shape of the worldsheet not a flat one. ????????? Please help me out. If you can't (or don't want to) my questions, maybe you know some forum or text where it can be infered but please don't tell me the standard answer to browse the arXiv or Green, Schwarz, bla bla bla. Just tell me references where you know that I can find an answer.