The polar cap region was reconstructed for all magnetic local time on the basis of 'CORONAS-I' data obtained in March-April 1994. Sporadic fluxes of relativistic electrons at high latitudes are studied. According to measurements of electrons with E∼0.5-1.3 MeV we can make conclusion about regions of closed geomagnetic field lines. Polar cap boundary locations and probability of electron flux appearances were determined for different Kp indices and were also the result compared with interplanetary parameters such as solar wind pressure and Bz component of interplanetary magnetic field. Ionospheric projections of last closed geomagnetic field lines were computed using the Tsyganenko-87W magnetosphere model. The relationship of the experimental polar cap boundaries to the model is discussed.