Based on the miscellaneous published radio and optical data, SDSS and APM catalogue we consider the various properties of the giant radio sources (gRS) with the aim of refining the conditions leading to the formation of these objects. We compare gRSs with the regular-sized radio sources in radio and optical bands, yielding the following results: 1. The fraction of broad line objects among gRSs with high excitation spectrum is the same as for the RSs from isotropic samples. According to Unified Scheme this leads to the isotropic angle distribution of gRSs jets, thus gRSs cannot be characterized as objects with jets lying in the plane of sky. 2. gRSs do not differ from normal sized RSs in apparent asymmetry distribution of their extended radio components (ERC). However the fact that asymmetry distributions for gRSs and giant radio quasars (gQSS) are essentially the same leads within the Unification Scheme to the conclusion that the origin of this asymmetry is in the non-uniform environment. 3. The richness of the environment for gRSs is the same as for normal sized RSs. This contradicts the opinion that the low density of the environment is the single reason for gRSs formation. 4. About 10% of FRII RSs have by order of magnitude longer lifetimes and eventually evolve to gRSs. 5. The observed relative quantity of radio quasars in gRSs population (~0.1) can be interpreted as the presence of long-living population of radio loud QSSs as ~0.1 of all radio quasars.
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