for large area resource inventories. All possible sources of data for 
measurement or estimation of the parameter of interest, from satellite 
imgery; small, medium and large scale aerial photography; and ground 
data are considered. An optimum mix, considering the detail of infor- 
mation possible and costs of data acquisition and information extraction 
at each stage, is selected. This often involves a fairly quick, cheap, 
general interpretation on small scale data, and the selection of sample 
areas for the collection of large scale and/or ground data for detailed 
measurement based on the initial interpretation results. In true multi- 
stage or multiple sampling, the selection of areas for detailed sampling 
and the expansion of detailed measurements to the entire survey area are 
based on quantitative statistical processes. This is in contrast to the 
more common practice of merely using detailed ground measurements in a 
general qualitative fashion to verify or adjust image analysis results.