5) Dividing the control unit automatically
Utilizing the overlay analysis of ArcGIS, this spatial model
could divide corresponding control unit for each function zone
automatically, based on the intersection relationships between
the two figure layers of the river function zone and
administrative district (county, town). More complete control
unit could be divided when the input-response relationship
between the pollution sources and the function zone, the point could be found out. The continued change of the function
zone’s water quality could be expressed by graphic using the
interpolation analysis technique (Fig. 6). To those function
zones applying one dimension or two-dimension models, the
spatial continued change of water quality could be expressed
with grid images in two dimension or three-dimension.