11
Information Hiding for Spatial and Geographical Data
Maria Calagna and Luigi V. Mancini
University of Rome “La Sapienza”, Rome (Italy)
11.1 Introduction
A geographical information system (GIS) represents geographical and spatial data
through digital maps that are built according to a specific representation model. A
digital map represents a set of features that are stored as couples < attribute, value >
for each position in the map. These features may be organized into different layers in
the map. Each layer logically represents a set of elementary features that can be used
in a specific working activity, or they can be used in addition to other features belonging to other layers. Figure 11.1 illustrates the abstract representation of a GIS as
a collection of different layers. In this example, the digital map is composed of four
layers: a spatial coordinate system layer, a regions layer, a rivers layer, and a towns
layer. All of them may be visualized together or separately. Also, features that belong
to different layers may be selected by the user and some operations can be performed
over them in order to obtain a new digital map. This is a distinguishing property of
GIS. Thus, digital maps can be visualized according to GIS users’ preferences, that
is, GIS users may select some features to proceed with their working activity, or they
can compose new layers starting from the ones that they have. For example, if a user
is interested in visualizing the rivers, which go through the eastern towns, first, the
user should select the features from the towns and rivers layers properly, and then
the user should be able to create a new map that visualizes a new layer containing
the rivers features that correspond to the user query.
In recent years the development of communications in terms of technology and
applications has influenced several domains in the public sector, including finance,
marketing, arts, and administrative services. The main relevant events include the
spreading of satellite and mobile communications. Consequently, Web-based applications are emerging to make information available to public and private clients. The
technology evolution improves the cooperation between the public agencies and the
efficiency of public and private services. However, while the technological advances
help people to access public information and public services more easily, on the
other hand, new problems about privacy and security arise. For example, a typical
risk concerns the fact that the data could be captured by unauthorized users. Thus,
Information Hiding for Spatial and Geographical Data
Maria Calagna and Luigi V. Mancini
University of Rome “La Sapienza”, Rome (Italy)
11.1 Introduction
A geographical information system (GIS) represents geographical and spatial data
through digital maps that are built according to a specific representation model. A
digital map represents a set of features that are stored as couples < attribute, value >
for each position in the map. These features may be organized into different layers in
the map. Each layer logically represents a set of elementary features that can be used
in a specific working activity, or they can be used in addition to other features belonging to other layers. Figure 11.1 illustrates the abstract representation of a GIS as
a collection of different layers. In this example, the digital map is composed of four
layers: a spatial coordinate system layer, a regions layer, a rivers layer, and a towns
layer. All of them may be visualized together or separately. Also, features that belong
to different layers may be selected by the user and some operations can be performed
over them in order to obtain a new digital map. This is a distinguishing property of
GIS. Thus, digital maps can be visualized according to GIS users’ preferences, that
is, GIS users may select some features to proceed with their working activity, or they
can compose new layers starting from the ones that they have. For example, if a user
is interested in visualizing the rivers, which go through the eastern towns, first, the
user should select the features from the towns and rivers layers properly, and then
the user should be able to create a new map that visualizes a new layer containing
the rivers features that correspond to the user query.
In recent years the development of communications in terms of technology and
applications has influenced several domains in the public sector, including finance,
marketing, arts, and administrative services. The main relevant events include the
spreading of satellite and mobile communications. Consequently, Web-based applications are emerging to make information available to public and private clients. The
technology evolution improves the cooperation between the public agencies and the
efficiency of public and private services. However, while the technological advances
help people to access public information and public services more easily, on the
other hand, new problems about privacy and security arise. For example, a typical
risk concerns the fact that the data could be captured by unauthorized users. Thus,