Administrative units are often seen as temporally stable. However, this is not the case.

A number of spatial and societal changes may occur, e.g. boundary changes, name changes as well as changes in administrative structures.

The aim of the DigDag project is to establish:

• A uniform research infrastructure within history, archaeology, place-names, statistics and geography. A digital cartographical skeleton for thematic mapping and analysis which will generate  new interdisciplinary research and make existing research more efficient.
• A historical-topographical-administrative search facility aimed at aiding visitor queries and of administration. An internal and internet-based service which the (major) cultural heritage institutions may relate their topographically ordered collections.
• An internet based reference work (a webGIS), which also contains a potential for administrative practising, e.g. within the fields of environment, cultural heritage and physical planning.

Key issues will be the generation of administrative units, generation of  geographical structures and providing adequate usability and searchability.

Data and archival material

The amount of available historical archival material is exceedingly large. The current digitisation process has primarily been oriented towards archival registers and not on the archival source material itself, although this is an emerging field. Thus, a number of digital registers have been established, directed at internal search/research functions at the local institutions, but which do not have any direct relation to or correlation with similar registers at other heritage institutions.

A substantial number of the digitised archival registers use, among others, a geographical/administrative entrance. The entrance is usually a topographical code (e.g. settlement, parish) or local authority jurisdiction (e.g. customs service, police districts). Due to changes in the administrative divisions, most of the geocodes are unique to each archive, or archival system.

Administrative data pose a number of problems on their own, since administrative divisions are dynamic over time as well as spatially. Seen over centuries, public and ecclesiastical administration becomes increasingly complex, resulting in ever increasing needs for updates in administrative divisions. An example is the most recent Danish administrative reform of 2007, superseding the radical 1970-reform after 37 years, itself preceding the jurisdictional reform of 1919. Because of the new administrative reform of 2007, comprehensive digital administrative divisions are available for the two most recent reforms. Thus, the need for a thorough digitisation of historical administrative divisions has become more urgent, as fewer and fewer researchers, public officers and people in general have a basic knowledge of previous administrative divisions.