Tests performed on the early images demonstrated that the 
photographic resolution of low-contrast MSS scenes is between 
200 and 250 meters (2). 
There has been an enormous amount of experimentation and doc- 
umentation demonstrating the multispectral approach to interpretation 
of terrain features (3,4). The digital image processing techniques - 
originally developed for planetary missions - have been extended to 
include not only photometric and geometric corrections but also semi- 
automatic classification of land cover, and in some cases location of 
probable mineralized zones (5). 
A number of experimental projects have been conducted to 
demonstrate the cartographic utility of the Landsat imagery. The 
principal organization concerned with this effort has been the U.S. 
Geological Survey. Black and white mosaics, single band mosaics 
printed in sepia, and multi band mosaics in color infrared response 
have been printed at scales of 1:250,000, 1:500,000, and 1:1,000,000. 
Formats have ranged from single Landsat scenes, to standard 12 x 29 
quadrangles, to entire states (6,7). It has been demonstrated that 
by fitting a slightly distorted UTM grid to identified control points 
in a single image or mosaic, coordinates of discrete points can be 
referenced to National Map Accuracy Standards at 1:250,000 scale (8). 
A new map projection, specially designed for Landsat imagery has been 
proposed (9), and current Landsat.imagery is being produced on this 
Space Oblique Mercator Projection. 
Landsat imagery has proven particularly valuable for barren areas 
like Antarctica (10,11) and northern Canada (12) where the princípal 
map information is the physiographic form of the Earth's surface. The 
major impediment to the widespread cartographic use of Landsat is the 
low resolution which makes it incapable of consistently showing the 
cultural features required for a map of any scale. The most useful 
products have employed Landsat imagery as a base at 1:500,000 scale 
with an overprint of cultural detail shown by conventional line map 
symbols. 
In four years of operation by Landsat-]l and a year and a half 
by Landsat-2, nearly complete coverage of the world's land areas has 
been obtained. A set of seven index maps showing worldwide coverage 
has been prepared by the U.S. Geological Survey (13), and a more 
descriptive index for the developing countries has been published by 
the World Bank (14). 
Skylab 
In April 1973, the United States launched the Skylab into a 
435 km circular orbit at 50° inclination. Three-man crews were 
launched in May, July, and November and occupied the laboratory for 
a total of 174 days. Skylab carried an Earth Resources Experiment 
Package (EREP) which included three imaging systems (15). 
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