tions where data may have been collected. Thus, the data must be extrapolated in 
order to evaluate criteria attainment for the larger spatial unit that the data represent. 
For the Chesapeake Bay and its tidal tributaries, using a grid-based spatial interpola¬ 
tion software provides a common spatial framework and spatial extrapolation. Spatial 
interpolation provides estimates of water-quality measures for all locations within a 
spatial assessment unit. This is accomplished at any single location by linear interpo¬ 
lation of the data of all its nearest neighbors. This approach provides an estimate of 
the water quality measure at all locations within the spatial unit being considered. 
An example of the use of spatial interpolation is illustrated in Figure VI-2, which 
displays the monitoring segment boundaries and fixed-station locations in the area 
Figure VI-2. Chesapeake Bay Program segment boundaries, fixed monitoring station 
locations and summer chlorophyll a concentration (pg liter 1 ) distribution in the Tangier 
Sound area of the Eastern Shore of Maryland and Virginia. Summer chlorophyll a 
concentration distribution is defined by spatial interpolation. 
chapter vi • Recommended Implementation Procedures 
