Positions, Networks, Fields, and Transformations - A Primer of GIS: Fundamental Geographic and Cartographic Concepts - page 177

ships into account, but the storage of the GI representation type usually uses
raster data structures. This should always be considered when working with
field data. It is easy, but wrong, to interpret raster cell boundaries as the
sharp boundaries between different attribute values, when, in fact, the geo-
graphic things and events represented by a field are nondiscrete.
A triangular irregular network (TIN) is a specific format for the repre-
sentation of fields that relies on a network of lines connecting sampled
points with known values. The connections form a Delauney triangulation,
which means that each point is connected to only two other points to create
triangular faces. This type of GI representation is most commonly used for
the visualization of elevation data, but can be used for any data that is col-
lected using irregular samples in an area. Dynamic versions of TIN make it
possible to rapidly change the TIN. The changes can be so rapid that
dynamic TIN holds potential to help train people for complex navigation sit-
uations.
Transformations
Even if GI is represented as a field, it may not originate with data collected
for every point in the area of the field. Since this detailed data collection
would be practically impossible, most field data is usually the result of trans-
forming position-based GI observations and measurements. For instance, a
property of soil, pH, shown as a nondiscrete field for an area, may be based
on an interpolation of soil samples collected at various points. The soil pH
data could be transformed back into a position-based GI representation as
contours that show where soil pH changes (e.g., a contour for every 0.5
change in soil pH). Transformations can be applied to any representation of
GI. GI can be transformed to different types—for example, positions to
fields, or networks to positions, or from one position-based GI representa-
tion to another (e.g., points to lines).
Two examples of field GI. On the left a DEM, on the right GIRAS land use.