When good maps are available but are too old, it is possible to re-use some elements rather than start with a map from scratch.
Some elements of a topographic map are more stable in time: significant changes in the relief, in parts of the river network, etc. are relatively stable compared to the interval between successive map editions (ideally 10-20 years). These elements can then be re-used on the new map.
Of course, many changes will affect other themes on the maps: new roads, some administrative limits, and above all in Namibia, new buildings and human settlements. For these elements, a comparison between the old maps and the new situation (as seen on recent aerial photos) will be required.
This approach was selected for the new topographic maps of Namibia, because a complete coverage at scale 1:250’000 and 1:50’000 done before Independence existed for the whole country.
This approach is fully justified for cost reasons, but it has the disadvantage to base the new map on an existing one produced without the technological improvements observed in the recent years (digital mapping, and above all, GPS surveying).