Database Reference
In-Depth Information
10.2.1 Geospatial Data Models and Representations
Depending on the application domain and collected geospatial information,
geospatial data can be modeled and represented in different ways. The two
most common approaches to model geographic information are using either
an
object-based model
or a
field-based model
.
16
,
17
In an object-based model, ge-
ographic objects correspond to real-world entities (also called
features
) about
which information needs to be managed. A feature typically has two parts: (a)
a spatial component (or
spatial extent
), which specifies the shape and location
of the object in the embedding space; and (b) a descriptive component that
describes the
nonspatial properties
of the feature in the form of attributes.
The spatial extent of an object is typically modeled as a point, polyline, or
polygon, depending on the required spatial granularity and scale of the data
to be managed. For the representation of a collection of features, different
approaches exist, such as the network model, spaghetti model, or topological
model.
16
The left part of Figure 10.1 shows an example of an object-based
presentation of geographic information (a road network).
In field-based approaches, the space to be modeled is partitioned (tessel-
lated) into two- or multidimensional cells, a cell having a spatial extent. With
each cell one or more attribute values are associated, each attribute describing
a continuous function in space. A typical example of field-based data are mul-
tispectral or hyperspectral raster imagery obtained from remote-sensing in-
struments. Field-based data are also common as outputs of simulations where
with each point in space a set of attribute values (measurements) is asso-
ciated. Note that in a field-based model, there is no notion of objects but
observations of phenomena in space, which are described by attribute val-
ues (measurements) that vary with the location in space. The right part of
Figure 10.1 shows an example of a field-based representation (estimated tem-
perature over an area).
Road system
in California
Temperature map
for California
Figure 10.1
(See color insert following page 224.) Examples of object-based
(left) and field-based (right) geospatial data representation.
