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Finally, & field check has been carried out. Results of the interpre- 
tation are shown in Fig. 1. Only the main land-use classes have been 
mapped here. 
The USEMAP interpretation was intended and produced as a full, 
highly detailed land-use interpretation. Thanks to this detailed 
interpretation, it was possible to aggregate the 65 original classes 
into 2 classes urban/non-urban that coincide closely with the urban/ 
non-urban classes that digital processing could provide for Landsat. 
4. Delineation of the urban area from Landsat 
The method used to define the urban area has been application of 
principal component analysis. This method has been described in 
MULDER (1975) and in DONKER and MULDER (1977). The various steps in 
the method are indicated in Fig. 2. 
The information of the original 4 bands of the Landsat frame taken 
on 22.03.73 is reduced to 2 principal component (pc) maps containing 
nearly all the original information. Each pixel may now be plotted 
in à 2-dimensional 'feature space diagram! according to its values for 
pcl and pc2. 
If representative pixels are sampled for selected land uses, they may 
form separate clusters in the feature space diagram. If a cluster is 
not mixed with other clusters, it means that the land uses can be 
easily separated spectrally. 
Fig. 3 gives the feature space diagram for the Enschede area. The 
clusters forming the urban area (residential, industrial and water) 
are overlapping; the clusters for forest and agriculture are separate. 
It is now possible to construct a 'separation line' (S4 in Fig. 3) 
that separates the urban land uses from the rural land uses. 
The following step is to produce a thematic map of the urban area 
by printing black all the pixels that are located in the feature 
space above the separation line and blank all the pixels below the 
line.