Database Reference
In-Depth Information
How can trajectories' footprints in the web be retrieved? (Section
16.4.3
)
What are the possible sources for uncertainty (with respect to the location
information)? (Section
16.4.4
)
16.4.1 Location: From Real World to Geo-Social World
We refer to “content” as any piece of information (such as text, image, audio,
or video, in any possible format) that it is possible to publish on the web as
a resource. Content is generated by a person (that represents him/herself or a
broader entity, such as an enterprise or an agency) using a device. The content
describes a real/abstract object/event. Based on the Oxford English Dictionary
definitions of “real” and “event,” we refer to a real object/event as “actually
existing as a thing or occurring in fact; not imagined or supposed.” A real object
is a perdurant entity in the world such as a mountain or a building and a real event
is “a thing that happens or takes place, especially one of importance” in a specific
place in a limited amount of time, such as a forest fire or a football match. We
refer to abstract object/event for every other type of information, including mood
and feeling description, such as messages like “I really feel good, today.” Even
if abstract object/event can have associated geographic coordinates, we limit the
discussion to the real objects/events and we call them
features of interest
.In
Figure
16.3
we can see three levels: the real world, the content, and the social
web levels, and the relations among objects in the different levels. The entities
in the bottom part (the real world) are the person, the device, and the feature of
interest. Each of them has a spatial location and an extension.
Any information produced is called content. A piece of information asso-
ciated to a content describing some properties of the information is generally
referred to as metadata. A geographic content, or CGI, has associated
geospatial
information
that represents a spatial reference and geometry in any format. In
other words, the metadata also contain the geographic reference. The metadata
can be automatically generated by the device (such as the date for a digital photo)
or manually added by a person (such as the title or the tags). A GPS device can
record the coordinate of the device and associate the geographic information to
the content metadata. Content can also include
implicit geographic information
such as place name in a textual message or the object represented in a photo.
The implicit information can be made explicit using different applications and
strategies and added to the content as metadata. The content with its metadata
is published on the web and becomes
published content
: a shared resource for a
certain community. At the web level it is also worth noticing that a person has
a virtual identity. His or her personal information on the social web can include
geographic information related to his or her usual living place, visited places,
and/or actual location. We call them
geographic user information
. These data,
especially the actual position, can be manually set or automatically updated from
