To provide context for this discussion, it might be useful to review recent figures on the
magnitude of this
activity. Daratech (1994) reported total sales by the GIS software industry of $450 million in
1993. A survey by the U.S. Office of Management and Budget reported annual expenditures on digital
geographic data activities within the federal government alone of $4.5 billion. Estimates of the
total annual value of U.S. activity range as high as
$10-14 billion.
The digital world of geographic data processing is very precise. The term "single precision"
implies about
1 part in 107, but many GIS vendors now offer double precision storage and manipulation of
coordinates and data, or 1 part in 1014• In the largest possible coordinate system for
geographic data, one covering the entire Earth, 1 part in 10 14 implies a need for positional
accuracy of about tQ-7m, which is about the size of a molecule. None of our measuring instruments
are capable of capturing data that even approach that level of accuracy, so why do GIS vendors
perceive a market for it? Does the GIS user's sense of accuracy depend more on the machine's
precision than on the accuracy of the data source?