Global Positioning System Reference
In-Depth Information
benefits (as outlined in Section 4.9). Some services such as Meetro are already
operational [14].
8.3
Some Digital Mapping Basics
8.3.1
Maps as an Interface
When one is considering digital maps there are two aspects to keep in mind; first,
the map that is seen and used via a human interface, and second, underlying
information that will usually be contained within a well-defined data format. Both
are described as maps. The image of a map seen on a computer screen is created
by an array of colored dots (or pixels) and is similar to the same map when printed
on paper. These are know as raster images and are an important part of computer
multimedia but are there primarily for the benefit of people. Images can be
superimposed easily and points of interest (PoI) can be plotted on the map to help
find facilities.
8.3.2
Invisible Maps
The mapping metaphor has been taken over by computer scientists to refer to the
activity of structuring any data conforming to some sort of reality, but in this case
we are considering the mapping of maps (i.e., structuring geospatial information).
The drawbacks of computer images are that they are inefficient to store and
manipulate and do not form an “information space.” Information spaces in
computer science refer to an abstract view of structured data that is often
contained within a database. If the information is coded within a normalized
structure, it may be used by software directly.
Machine-learning techniques are being found to convert pictures into more
structured formats: examples include automatically picking out roads from an
aerial photograph and turning a vehicle number plate image into plain text (to be
inserted automatically into the congestion charging ticket!). Often the process of
structuring is done manually, for example, with a digitizing tablet. Once captured
the information is described in a parametric form (or metadata). A straight line on
a 2D map could be described by two sets of x-y coordinates and a curved line
either by a set of coordinates or as a mathematical function seeded by a subset of
points (see the Epilogue for a more detailed explanation). This sort of map is
known as a vector map. In mathematics, a quantity with a size (or magnitude) and
a direction is defined as a vector. Most digital maps therefore have an underlying
vector format with a rendering process that is used to take a required subset of the
vectors and to render it into a raster image that can be displayed or printed.
