The reference surface in relation to which the heights in the Republic of North Macedonia are expressed coincides with the mean level of the Adriatic Sea determined on the basis of tide gauge measurements carried out at tide gauges in Koper, Rovinj, Bakar, Split, Dubrovnik and Bar, along the Adriatic Sea, in the period from 1962 to 1980. The reference surface for defining ellipsoidal heights is the level ellipsoid of the GRS 80 reference system.