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As part of their foundational mission, libraries keep historic maps. Maps are subject of research with respect to their role as cultural texts, promotional devices, instruments of sovereignty or authoritarian images and they are subject of scientific research. Making these resources available to the public while preserving them is a challenge librarians worldwide are tackling based on modern technologies.

Due to their spatial nature, historic maps deserve special treatment as library resources. Accessing historic maps and relating them to others (modern or historic as well) improves and accelerates research. This is demonstrated by well known historic maps examples like:

• The Lienzo de Quauhquechollan dates from the 16th century and it is perhaps the oldest map of Guatemala. This map tells a conquest story from the indigenous viewpoint instead of the Spanish Empire's perspective. Unlike traditional snapshot-like maps, the Lienzo represents the history of a geographic region depicting complex spatio-temporal interactions. Handling the Lienzo is difficult because it is composed of 15 cotton pieces but they have been scanned and digitally restored in a project ran by the Universidad Francisco Marroquin in Guatemala City.
• The map of Napoleon's march of 1812 over Russia. This Charles Minard's map is a valuable tool for understanding the development and consequences of such a war campaign. This map combines space, time, temperature and the number of soldiers to show the catastrophic loss of life in Napoleon's Grand Army.
• The map of 1854 cholera outbreak in London by John Snow. The story surrounding this map is almost legendary and well-known in the fields of public health, medical geography, history of medicine, geography and cartography. This map displays cholera victims and water pumps suggesting clustering around a specific pump; it is also believed the map showed how an illness is dispersed, to change public health policy and to probe Snow's hypothesis regarding water-transmitted cholera instead of the prevailing miasma theory of that time. Most of these historic assertions are matter of debate today.

Each of the example maps represents geographic features and people interactions framed as historic events which are difficult to detail using bare text. They not only depict space but also summarizes complex interactions of people with their environment. Details like the Lienzo is emphasizing storytelling sacrificing spatial precision or the fact that Minard preferred data representation accuracy over precise geographical position or the mismatching death count on different version of Snow's map cannot be acquired only by looking at the maps. Similarly, reading documents without observing the maps does not provides a full understanding of the events. For example, linking the historic map of London's cholera outbreak of 1854 to John Snow would help a library user to discover that there are different maps claiming to be the John Snow's map.

Academic and scientific research could be improved by including maps as part of result sets on libraries searches. However users searching through library records usually face a gap: Their results consist of written text or images, and their search is based on key word matching, not on the actual geographic contents represented in these images. It would be favourable if search was based on explicit representations of geographic contents instead. This thesis address this gap through the use of Linked Open Data as a means to enable librarians to improve historic map descriptions and allowing them to relate maps to other data sources which improves its discoverability and understanding.

For a detailed description see A LOD-based georeferencing tool for historic maps