Real-world features exist in two basic spatial forms: objects and phenomena.
Objects are discrete and definite, such as building, highways, cities, and national parks.
Phenomena are distributed continuously over a large area, such as terrain,
temperature, rainfall, noise levels, and other environmental indices.
14
Geographic data depict the real world in
the two basic forms, leading to two
distinct approaches of representing the real
world in geographic databases:
1) Object-based model: the basic
spatial units are discrete and
identifiable, represent as vector data
model (points, lines, and polygons).
2) Field-based model: phenomena are
real world features that very
continuously over space with no
obvious or specific extent. As the most
commonly used type of tessellation is a
finite grid of square or rectangular cells,
field-based database are generally
labeled as the raster data model
(grid)