The irregular structure of the high-latitudinal, mid-latitudinal and equatorial ionosphere from the topside sounding on board Intercosmos-19 satellite is investigated. The features of the topside ionograms connected with the large-scale structure of the ionosphere (polar hole, day side cusp and trough, main ionospheric trough, ring ionospheric trough, equatorial anomaly, and Brazilian geomagnetic anomaly) are shown. The additional traces connected with the media-scale irregularities (horizontal gradients of a density, peaks of a concentration, ionospheriс holes in foF2 and hmF2, slanting layers, and sporadic layers over the F2 maximum) are revealed. The examples of the waveguide propagation in the high-latitude and low-latitude ionosphere are presented. The different types of the aspect scattering on the small-scale irregularities are divided. The global distribution of the F-spread occurrence probability for the different geophysical conditions is built.