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combine services. Semantic annotations have been proposed to lift existing geo-
data to a semantic level [56,72]. In context of digital humanities research, anno-
tations have been applied to create Linked Spatiotemporal Data, e.g., to enrich
old maps with interlinked information from the global graph [89]. With respect
to OGC's family of Sensor Web Enablement standards (SWE), researchers have
developed sensor and observation ontologies, semantically-enabled versions of
OGC services such as the Sensor Observation Service (SOS), or RESTful trans-
parent proxies that serve Linked Sensor Data [20].
In this section, we identified and described seven important research questions
being asked in the field of geo-semantics (listed in Table 2).
5Conluon
We have argued that the relevance of geospatial information lies in the useful-
ness of geospatial referents, such as places, events, and geographic objects, and
their spatiotemporal relations, which allow systems to indirectly localize and in-
terlink numerous other resources in the Semantic Web. In part, this importance
of geospatial information is reflected by the fact that the few already existing
geo-data repositories, e.g., Geonames, have become central hubs on the Web of
Linked Data. In addition, other key repositories, such as DBpedia, Freebase,
and so forth, contain substantial collections of geo-data. However, we have also
illustrated that even though geospatial information has reference systems, which
allow one to precisely map and index the extent of geospatial referents, concep-
tualizing and formalizing these referents is an unsolved challenge. This challenge
is mainly due to the situated and multi-perspectival nature of geospatial phe-
nomena. It calls for semantic strategies that allow highlighting, distinguishing,
and linking of the different perspectives to the localities that are inherent in
geo-data.
Geospatial semantics addresses this need with semantic modeling of geospatial
classes as well as semantic technology for access, comparison, and interlinking
of geo-data. Specific semantic modeling challenges include the notions of reso-
lution and scale in geo-ontologies, ontological perspectivity, semantic reference
systems, place reference, trajectories, event discovery, the formalization of spa-
tial relations, and the computation of spatial reasoning. Semantic technology for
access and retrieval include semantically enabled spatial data infrastructures and
Linked Spatiotemporal Data, as well as cognitively plausible similarity measures,
analogy-based reasoning, and translation tools for geo-ontologies.
References
1. Abdelmoty, A.I., Smart, P., Jones, C.B.: Building place ontologies for the seman-
tic web: Issues and approaches. In: Proceedings of the 4th ACM Workshop on
Geographical Information Retrieval, GIR 2007, pp. 7-12. ACM, New York (2007)
