CONCLUSIONS 
The techniques for data organization for interchange have progressed from 
specific formats, individually-defined in paper documents through definition 
of format families for similar data (LANDSAT CCT) to definitions of data 
modules. Concurrently, the ISO has defined a layered approach to the 
definition of the interchange process, which clarified the need for the 
separation of the format definitions from the generic format descriptions, 
ISO 8211 and the GDIL provide format descriptive approaches which may be 
used to describe any of the format structures defined by the various 
disciplines, allowing their data to be transferred between systems with a 
minimum of human intervention or special logging programs. 
LGSOWG experience has shown that the self-defining or descriptive approach 
often fails to result in the generality intended by the designers of a 
format. Typically, many users will implement one "instance" of the format 
family, ignoring all the information describing the structure in general. 
This is often the fastest, least expensive way in which to read the data 
from one particular source. With this experience in mind, groups developing 
nev standards will often shun the general formats (such as ISO 8211) because 
they have too much overhead for any specific application. 
ACKNOWLEDGEMENTS 
Development of the GDIL has been sponsored by the Information Systems Office 
of the (USA) National Aeronautics and Space Administration Office of Space 
Science and Applications. 
This report was partly written at the Jet Propulsion Laboratory, California 
Institute of Technology, under contract to NASA. 
The authors would like to acknowledge the efforts of all those engaged in 
the arduous task of developing and promoting standards. It is generally a 
thankless task, usually resulting in more criticism than praise. We would 
also like to thank David Harris of PCI for his thoughtful comments and 
editing of this paper. 
REFERENCES 
Billingsley, Fred C. (1985). General Data Interchange Language, 
Specification and related Documents. Jet Propulsion Laboratory, 4800 Oak 
Grove Drive, Mail Stop 168-514, Pasadena, California 91109. 
Canadian Council on Surveying and Mapping (1984). National Standards for 
the Exchange of Digital Topographic Data, Volume 1. 
Canadian Council on Surveying and Mapping (1985). Proposed Standards for a 
Digital Topographic Information Model. 
EOSAT (1985). User's Guide for Landsat Thematic Mapper Computer-Compatible 
Tapes, Earth Observation Satellite Company, Lanham, MD. 
Goodenough, D.G., Palimaka, J.J., Dickinson, K., Murphy, J. (1979). 
Standard Format for the Transfer of Geocoded Information in Spatial Data 
Polygon Files. CCRS Research Report 79-3, Canadian Centre for Remote 
Sensing, Ottawa, Canada. 
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