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Aims. We explore the outer Galactic disc up to a Galactocentric distance of30 kpc to derive its parameters and measure the magnitude of its flare.  Methods. We obtained the 3D density of stars of type F8V-G5V with a colourselection from extinction-corrected photometric data of the Sloan Digital SkySurvey - Sloan Extension for Galactic Understanding and Exploration(SDSS-SEGUE) over 1,400 deg^2 in off-plane low Galactic latitude regions andfitted it to a model of flared thin+thick disc.  Results. The best-fit parameters are a thin-disc scale length of 2.0 kpc, athin-disc scale height at solar Galactocentric distance of 0.24 kpc, athick-disc scale length of 2.5 kpc, and a thick-disc scale height at solarGalactocentric distance of 0.71 kpc. We derive a flaring in both discs thatcauses the scale height of the average disc to be multiplied with respect tothe solar neighbourhood value by a factor of 3.3^{+2.2}_{-1.6} at R=15 kpc andby a factor of 12^{+20}_{-7} at R=25 kpc.  Conclusions. The flare is quite prominent at large R and its presenceexplains the apparent depletion of in-plane stars that are often confused witha cut-off at R>15 kpc. Indeed, our Galactic disc does not present a truncationor abrupt fall-off there, but the stars are spread in off-plane regions, evenat z of several kpc for R>20 kpc. Moreover, the smoothness of the observedstellar distribution also suggests that there is a continuous structure and nota combination of a Galactic disc plus some other substructure or extragalacticcomponent: the hypothesis to interpret the Monoceros ring in terms of a tidalstream of a putative accreted dwarf galaxy is not only unnecessary because theobserved flare explains the overdensity in the Monoceros ring observed in SDSSfields, but it appears to be inappropriate.

Flare in the Galactic stellar outer disc detected in SDSS-SEGUE data