In this paper we show that the geometrical configuration of the auroral electrojet is of great importance in the interpretation of Doppler velocity data obtained by auroral backscatter radars operated close to the auroral oval at low elevation angles. We show that some of the characteristic features in the azimuthal dependence of the radar Doppler velocity can be explained by accounting for the auroral electrojet curvature produced by (1) the shape of the auroral oval, (2) the altitude variation of the Hall and Pedersen currents, and (3) other local variations in current flow. An important application of the geometrical considerations described in this paper is the estimation of the ionospheric electric field from Doppler-velocity variations observed in the diffuse radar aurora.