Origin of maps in this database
All maps in this database have been published by the United States
Geological Survey under contract to the National Aeronautics and Space
Administration. These maps were originally published between 1971 and 1998.
The intent of this web site version of those maps is to provide a planetwide
summary of the geology of the best-know planets and satellites (Mercury,
Mars, and the Galilean satellites Io, Ganymede, and Callisto) for which
a comprehensive set of maps exists. Venus and Europa are still in the process
of being mapped. Although images of the outer plants' satellites have been
obtained, they are rarely at a resolution allowing detailed geologic mapping,
and therefore have not been created and published in the USGS I-map series.
The Cassini mission, now on its way to Saturn, will provide much-improved
images of Saturn's satellites.
Digitization of the maps
Most of the maps were layed out using traditional photo-mechanical
and paste-up methods in preparation for printing. Where possible, the press-reading
stable-base films were scanned. In some cases, maps had to be digitized
from paper copies. In both cases, maps have been rectified by means
of control points in order to minimize any distortions.
Map unit colors
Due to differences in the way different programs handle color, the
geologic map unit colors may differ from file to file, particularly, those
in the ARCView project format may differ significantly from the TIF, PDF,
and Illustrator* files.
The maps reflect the knowledge in hand at the time the maps were
originally made. This dataset is intended to be an archive of the geology
of these bodies as it was understood at the time the maps were completed.
No attempt has been made to update them based on re-analysis, new discoveries
or new mission data.
Typographical and paste-up errors recognized in the published maps have
been corrected, but there has been no reinterpretation of the analysis
that was done by the original author(s), even where new data have shown
interpretations to be dated.
* mention of trade names is not meant to imply endorsement by the USGS,
but is merely used for descriptive purposes.