209 
Ratings: + = good; 0 = moderate; 
3. 3.2 ERTS-1 interpretation, soil map Badajoz and soil map with API 
A second map was interpreted independently on an enlargement of a part of the 
former ERTS colour composite print at a scale of 1 : 250, 000. The field check 
in this area was considerably longer: 7 weeks. A physiographic soil map of the 
Merida area with 24 mapping units based on the above interpretation is presented 
in fig. 4. The summarized results of the interpretation and field work showing 
physiography, vegetation/land use, and dominant soils (soil class acc. 7th. 
Approx. , USD A, 1967) may be found in the legend. 
A comparison was made with the existing soil map of the Province of Badajoz 
(C.S.I. C. , Madrid, 1968) scale 1 : 250,000, and also with a physiographic soil 
map scale 1 : 100, 000, based on aerial photo-interpretation and field check 
(ITC, student field work 1973). The results and discussion are presented in 
table 3. The comparison of the ERTS-1 map with the ITC soil map based on API 
is easier because both legends have a physiographic basis, while the Soil Map of 
Badajoz is mainly based on profile characteristics, though more detailed than 
those of the Soil Map of Spain. 
Conclusions regarding table 3 reveal that the ERTS-1 imagery interpretation was 
successful for 17 mapping units covering 3/4 of the whole survey area of the 
2 
Merida Region (1200 km ). Sub-divisions with a good measure of accuracy were 
possible in the alluvial valleys (A), the miocene clay (M). Further analysis was 
coincided well in the erosion terrace (O^), the complex of arkose, clay, and 
rarlas (0 2 ), the arkose (O^), and finally the undulating to rolling area on granite 
(G). 
Sh 
o The ERTS-1 interpretation was moderately successful in 7 mapping units, covering 
approximately 1/4 of the Merida Region as the lithology could not always be recog 
nized and delineated. This refers to the following areas: ranas (R), quartzite hills 
(Q), rolling on limestone (F), and undulating to rolling on diorite (D). More obser 
vations in these areas would be needed. 
4. GENERAL CONCLUSIONS 
ERTS-1 imagery promises to be very valuable for generalized to exploratory soil 
surveys at small scales up to 1 : 500, 000, valuable for reconnaissance surveys 
at scales up to 1 : 100, 000 and useful at scales up to 1 : 50, 000 in conjunction 
with conventional aerial photo-interpretation. Moreover it seems to be a valuable 
tool for updating existing soil maps at scales as mentioned above.