The spatial distribution and temporal dynamics of power frequency electric and magnetic fields in Saint-Petersburg, Kazan, Belgorod and Petrozavodsk has been studied. It is established that electric fields of significant strengths occur near high-voltage transmission lines (HVTL) only. It is found that sanitary-protection and exclusion zones of the standard size do not always ensure a decrease in electric field strength to maximum allowable levels on their boundaries. Thus, the electric field intensity of four 4 HVTL in St. Petersburg increases due to the mass construction of multi-storey housing leading to an increase in power consumption. A dependence of the electric field strength on meteorological factors was also determined, primarily on air humidity (direct dependence), and on atmospheric pressure (indirect inverse relationship). The power frequency magnetic field produces a variable city-wide background caused by a set of sources. The more intense is the technogenic load, the higher is magnetic induction, which renders it a convenient geoindicator for mapping. Also, the indicators of magnetic induction reflect the characteristics of power networks. Abnormally high values of magnetic induction were recorded in all cities, which are explained by the influence of electric cables. No exceedances of allowable levels of magnetic induction in residential areas were observed.Keywords: electric fields, strength, magnetic fields, magnetic induction, high-voltage lines, monitoring, mapping.