The ultraviolet and optical spectra of the active galaxy NGC 5548 were taken from the active galactic nuclei watch database in the 1993 monitoring campaign. The ratios of the line intensities of C IV to Lα and at Lα to Hβ have been measured at different parts of the line profiles. Both ratios are at all times high in the low-velocity centre(s) of the lines but decrease in the high-velocity wings. Theoretical modelling of the two C IV-to-Lα and Lα-to-Hβ ratios using the standard photoionization code CLOUDY show that the observed line ratios can be accounted for by a system of clouds illuminated by the central source and located at different distances from the centre. The possible geometry of NGC 5548 is discussed.