A unique macroseismic data base, in the form of Intensity Data Point (IDP) maps, is available for some of the seismic events which have occurred in Italy since 461 A.C. The problem of the reconstruction of the isoseismal shape imposes rigorous requirements on the quality of intensity data. We present here a collection of 55 IDP maps in isolines which, to various degrees, meet our quality requirements to analyze the shape problem. Our generalization of an IDP map in isolines is unconventional, and is based on the new approach. The methodology, along with the smoothing method for IDP maps (Modified Polynomial Filtering, MPF), uses the Diffused Boundary (DB) method, which visualizes the uncertainty of isoseismal boundaries. We define a quantitative measure of the isoseismal uncertainty and classify the isoseismals for all selected events. The presented collection of isoseismals can be used for comparison between observed and theoretical isoseismals. This comparison involves simultaneous testing of crustal and source models. The collection gives a sufficiently accurate idea of the quality of the isoseismals of Italian earthquakes; it can be useful for space local control of the intensity measurements as well.