A measurement method and system are presented for in-line measurements of one or more parameters of thin films in structures progressing on a production line. First measured data and second measured data are provided from multiple measurements sites on the thin film being measured, wherein the first measured data corresponds to first type measurements from a first selected set of a relatively small number of the measurement sites, and the second measured data corresponds to second type optical measurements from a second set of significantly higher number of the measurements sites. The first measured data is processed for determining at least one value of at least one parameter of the thin film in each of the measurement sites of said first set. Such at least one parameter value is utilized for interpreting the second measured data, thereby obtaining data indicative of distribution of values of said at least one parameter within said second set of measurement sites.