The Archivio di Stato di Milano (the National Archive of Milan) has begun the digital archive process of historical cadastral maps few year ago, considered as the first step to support their on-line publications. The portal project ‘Atlas of historical cadastral maps’ was made upon a collaboration between Politecnico di Milano -DIIAR (leader), the two principal owners of the cadastral heritage, Archivio di Stato and Agenzia del Territorio – Direzione Regionale (the Agency of Territory – Regional Direction) and Regione Lombardia – Giunta Regionale Presidenza, Patrimonio e Sistema Informativo (Lombardy Region), for the indication activities and those of decentralization of the territory. The main aim was to put together cataloguing approach and to guarantee the spread online presentation and diffusion of the geo-iconographic historical contents in a detailed territorial dimension. Considering that only for the regional area of Lombardy – interested by the project – there is an extraordinarily huge patrimony, constituted by thousands of sheet units, belonging to different documentaries series, produced during different periods by the cadastral offices devoted to the cadastral generation and conservation. The map documentation, nowadays conserved in the different Archivio di Stato offices decentred within the provinces of the Lombardy region, is statistically the most essential for consulting purposes, correspondent to a wide and variegate research spectrum. To have an idea of the regional coverage, the current cadastre and its plant (Impianto al vigente catasto, 1937-1958) -owned and conserved by Agenzia del Territorio - is made by about 70.000 sheet for each layer. The Atlas aims to provide for users an agile and intuitive access instruments to the historical cadastres and maps, navigating on currently available maps at different scales (i.e. the technical regional map 1:10000,or the IGM Military Geographic Institute) the territory of yesterday refereed to administrative boundaries losing correspondence with the nowadays territorial municipalities. A bond with the actual map can be well constituted by the first cartographic representation at the topographic scale of the Lombard territory anchored at a geodetic reference system: La mappa degli Astronomi di Brera (The map of Astronomi of Brera) and the ITM R LV, adopting an articulated semantics for the anthropic thematic issues of the territorial political-administrative boundaries. The Atlas in a multidisiplinary access networking approach, will be aligned to the international standard for the historic cartography (ISAD, EAD), and to the EU standard for geographic map sharing (INSPIRE); at the same time, being the maps historic geo-iconographic documents, they have to be compared to historic descriptive standard (AACR2_CM; ICCD for Italy).