that has been developed by the Canadian Centre fur emote Sensing. This system 
produces image CCT's where the pixel element has been resampled and rotated to 
conform to the orientation of the Universal Transverse Mercator projection used 
for much Canadian mapping. Each resampled pixel is 50 m square and the imagery 
contained in a DICS CCT covers four standard 1:50 000 maps. 
By appropriate density slicing of the DICS tape it is possible to produce on a 
raster scanner what is in essence, a water separation negative for a small-scal: 
map (figure 3). The water areas are now true to scale and in full detail. The 
only generalization that has occured is that resulting from to the limiting 
resolution of the Landsat system. When the mapped outlines of lakes at 
1:50 000 are superimposed on this image (figure 4) it is apparent that lakes as 
small as 150 m diameter are detected. 
MERGING CONVENTIONAL CARTOGRAPHY AND LANDSAT IMAGERY 
  
If more lake detail is to be shown on small-scale maps then the cartographic 
approach of outlining has to be dispensed with. The Landsat-derived water 
area can be substituted for the previously outlined and screen-filled water 
body by selecting a suitable dot screen percentage and ink colour that would 
make the feature legible without an outline. Drainage still remains an item 
for cartographic drafting since Landsat does not provide this information in 
sufficient detail. 
Merging the normal cartographic drainage with the water areas derived from 
Landsat to create the hydrologic information for 1:500 000 and 1:1 000 000 is 
shown for sample map sections ‘in ‘figure 5 (a). This is compared with the 
traditional hydrologic cartography for the same areas in figure 5 (b). There 
is little doubt that such a combination of traditional cartography and Landsat 
imagery can produce hydrologic mapping at small scale that is more descriptive 
of the country it portrays than conventional cartography alone. 
DIGITAL DATA BASE FOR WATER AREAS 
One of the side benefits of using digital Landsat data to map water bodies is 
that of the creation of a digital data base of water surfaces, which lends 
itself readily to the computation of the water area present in any region. 
This information is useful for agencies concerned with the total water resources 
as they effect both the human population and the wildlife population. The 50 m 
pixel size gives adequate resolution for large-area studies. Only the 1:50 000 ) 
map could provide greater detail, but this series is neither complete or infal- 
lible and digitization or measurement of water areas from this scale of map is 
a mammoth task not likely to be undertaken. 
CONCLUS LON 
The extraction of thematic information from Landsat MSS imagery and merging it 
with conventional cartography has been shown to be reasonably straightforward 
for water features. It provides one means of improving the cartographic ren- 
dition of these features on small scale maps where they form the dominant 
character of the landscape being mapped. 
The use of digital Landsat imagery for this purpose would additionally provide 
a data base from which water areas could be determined to an accuracy compara- 
ble to that of 1:250 000 mapping. 
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