Database Reference
In-Depth Information
6
Organizing GI as
Linked Data
6.1 INTRODUCTION
This chapter provides advice on how to represent Geographic Information (GI) as
Linked Data. We cannot hope to cover all aspects of this representation; the topic
is simply too broad for any one topic and individual experience. Therefore, we con-
centrate on some of the essential areas. The chapter explicitly examines identity,
classification, geometry, topology, and mereology through examples based on the
imaginary island state of the Merea. By the end of the chapter, you will be familiar
with common issues and how to identify and represent some of the more common
forms of GI. Those with little knowledge of GI will be more aware of its nature, and
those new to Linked Data will have a better understanding about how it should be
approached. The chapter paves the way for Chapters 7 and 8 concerning the publica-
tion and linking of Resource Description Framework (RDF) datasets and identifies
certain issues that cannot be fully resolved in RDF and RDFS (RDF Schema) but
can be better addressed by techniques using the OWL (Web Ontology Language)
ontology language and described in Chapter 10.
6.2 IDENTITY: DESIGNING AND APPLYING
UNIVERSAL RESOURCE IDENTIFIERS
We begin our story from the perspective of Merea's national mapping agency, Merea
Maps. When considering identity, Merea Maps needs to think about what it is inter-
ested in identifying with URIs (Uniform Resource Identifiers) and then think about
how to construct these URIs. Its two main products are a place-name gazetteer and
a detailed digital topographic map. We begin with the gazetteer, which identifies all
the named entities represented on the topographic map: settlements; sites and other
places (e.g., factories, hospitals, farms, etc.); buildings; roads; rivers; hills; valleys;
and so on. All these will need to be assigned a unique URI, as will any neces-
sary properties between them. The gazetteer is required to support a few topological
and mereological properties, such as “within” and “part of,” like “Medina is within
North Merea” and “Ash Fleet Farm House is part of Ash Fleet Farm.”
Let us first consider the identification of “things,” Merea Map's real-world fea-
tures, such as buildings, hills, and so on. The URI has essentially two components:
something to identify the domain and something to identify the thing within the
domain. The domain is the easy bit; if we suppose that Merea Maps has the domain
www.mereamaps.gov.me
,
then it could simply choose to use this. More typically,
though, organizations tend to make explicit the fact that the domain is about
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