Environmental Engineering Reference
In-Depth Information
Fig. 22.4 Basic design of
the media integration of
G-
CIEMS
. Data from different
media and different
geographical shapes joined by
projecting areas or length
between the grid cells,
catchments and river
segments (Suzuki et al. 2004)
l
Union
combines features from different layers
l
Merge
appends features of different files by attributes
l
Intersect
cuts features out of an input layer and joins the attributes
The latter is commonly used to aggregate information from one layer by objects
to another. Having interpolated precipitation as a grid and the geometries of the
catchments in an area, the information in a GIS can easily be intersected. The GIS
either calculates the mean value within (underneath) a geometry, adding this result
to the attributes of the file, assuming that the separate catchments will be modelled
as a whole; or
cuts
the intersection of the catchments and iso-surfaces of values
from the grid, assuming different allocations. The latter aspect requires that the
raster (or grid) is being converted into a feature file, following adjustable
preferences on classification of the values.
d) Spatial Aggregation
Aggregation aims at the simplification of data. It joins existing data based on their
characteristics by calculating parameters, for e.g. mean direction of currents,
maximum wave height.
Generalization aggregates objects by
combining
or
composing
them, based on
specific (spatial) attributes. Data from different sources or dissimilar measurements
can be calculated to a characteristic factor or typified in classes or ranges. Results of
these functions are new layers, larger than the input layers.
22.3.2 Handling Dynamics
Maps, the primary output of a GIS, are static representations of ecological systems
and landscapes, using the topography of their components. In contrast, dynamic
data contain changing numbers, positions and states of entities, altering their
quantities and qualities in space and time. Typically, series of point measurements
