@inproceedings{oded2006contour,
title={Contour lines of the two-dimensional discrete Gaussian free field},
author={Oded Schramm, and Scott Sheffield},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203352840250710},
booktitle={Acta Mathematica},
volume={202},
number={1},
pages={21-137},
year={2006},
}

Oded Schramm, and Scott Sheffield. Contour lines of the two-dimensional discrete Gaussian free field. 2006. Vol. 202. In Acta Mathematica. pp.21-137. http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203352840250710.