Cone spherical metrics are conformal metrics with constant curvature one and
finitely many conical singularities on compact Riemann surfaces. By using
Strebel differentials as a bridge, we construct a new class of cone spherical
metrics on compact Riemann surfaces by drawing on the surfaces some class of
connected metric ribbon graphs.Comment: 25 pages, 8 figures. Version 2: minor typo corrections; revised
according to referee's comments. We substantially revised the proof of the
second theorem to make its exposition easier to understand. We added a new
section, where we discuss on the Riemann sphere the consistence of metrics
generated by Strebel differentials with the two angle conditions by
Mondello-Panov and Eremenko, respectivel