  The paper is devoted to the questions connected with the investigation of the
S.P. Novikov problem of the description of the geometry of level lines of
quasiperiodic functions on a plane with different numbers of quasiperiods. We
consider here the history of the question, the current state of research in
this field, and a number of applications of this problem to various physical
problems. The main attention is paid to the applications of the results
obtained in the field under consideration to the theory of transport phenomena
in electron systems.
