English to Greek Tech/Engineering Electronics / Elect Eng Radio Propagation and radio coverage

Digital Terrain Elevation Data (DTED)
During the late 1980s Canada began leading the way with electronic maps that
could be interpreted and used by computer. They developed the Digital Terrain
Elevation Data or “DTED” series of maps for northeastern Alberta, near Cold
Lake. These were expanded and now cover most of Canada.
The original maps took “spot” elevations every 500 m from a 1:250,000 scale
map (1 cm = 2.5 km, or 1 inch = 6.3 miles).
The second generation of maps averaged the elevation over that same 500 m
square and provided the single elevation number for each 500 m square.
It was reasonably well known among radio people that within a 500 m horizontal
distance, larger hills were often missed and the original DTED maps were not
that accurate. They were not trusted for radio path design, specifically
microwave point-to-point links. They were used, however, for early coverage
plots of radio systems.