  We trace the cosmic web at redshifts 1.0 <= z <= 1.8 using the quasar data
from the SDSS DR7 QSO catalogue (Schneider et al. 2010). We apply a
friend-of-friend (FoF) algorithm to the quasar and random catalogues to
determine systems at a series of linking lengths, and analyse richness and
sizes of these systems. At the linking lengths l <= 30 Mpc/h the number of
quasar systems is larger than the number of systems detected in random
catalogues, and systems themselves have smaller diameters than random systems.
The diameters of quasar systems are comparable to the sizes of poor galaxy
superclusters in the local Universe, the richest quasar systems have four
members. The mean space density of quasar systems is close to the mean space
density of local rich superclusters. At intermediate linking lengths (40 <= l
<= 70 Mpc/h) the richness and length of quasar systems are similar to those
derived from random catalogues. Quasar system diameters are similar to the
sizes of rich superclusters and supercluster chains in the local Universe. At
the linking length 70 Mpc/h the richest systems of quasars have diameters
exceeding 500 Mpc/h. The percolating system which penetrate the whole sample
volume appears in quasar sample at smaller linking length than in random
samples (85 Mpc/h). Quasar luminosities in systems are not correlated with the
system richness. Quasar system catalogues at our web pages
http://www.aai.ee/~maret/QSOsystems.html serve as a database to search for
superclusters of galaxies and to trace the cosmic web at high redshifts.
