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LITHOSTRATIGRAPHIC MAPPING 
For an interpreter having no prior knowledge of the area, proper rock identifica 
tion proved to be a very difficult task. The units delineated on the final interpre 
tation were all detectable on the ERTS imagery, but identification was in most 
cases not possible before a certain amount of a priori knowledge had been acquired 
through the study of aerial photographs,comparison with existing maps, or by 
appropriate field checking. 
In general, lithostratigraphic mapping on ERTS imagery had considerable limi 
tations. Due to the variable lithology and the relatively small outcrop sites in the 
test area, continuous mapping was not always possible. It was found that outcrop 
ping sedimentary rock units should have a width of at least 150-200 meters in or 
der to be detectable. 
This figure holds for high-contrast alternations of stratified rock; with lower con 
trasts the boundaries will become increasingly more fragmentary and will finally 
disappear, causing coalescence of the images of adjacent rock units. 
Continuous delineation of lithological boundaries is hampered by low resolution. 
The resulting map often shows discontinous lines due to fragmentation of image 
elements. This leads to inaccurate delineation of lithological units: in order to 
obtain closure, simplifications have to be made, often resulting in boundary mis 
alignments. 
STRUCTURAL MAPPING 
The regional structure is mainly revealed by topographic relief expressing the 
morphology of folded mountain belts and intermontane basins. The pronounced 
topography of certain resistant rock units - such as the Paleozoic, the Upper 
Cretaceous, and the Jurassic - helps in the delineation of major structural trends. 
Numerous structural closures can be detected on the imagery. Correct identifica 
tion of the real nature of the folds is severely hampered due to the low image re 
solution, which causes diagnostic shape elements, such as flatirons, dipslopes, 
hogbacks, and strike ridges to become invisible or unrecognizable. 
Fold structures of sizes smaller than 2 kilometers across usually become too 
vague to be recognized with sufficient reliability. Typically, mapping of fold 
structures can mainly be done in terms of delineating structural trends. Such 
trends are reflected by the morphological expression of certain lithological types 
and to a lesser degree by variations in tonal differences due to different rock/soil 
colourations or to selective vegetation and land use.