HISTORY OF GEODETIC DATUM

Elevations (benchmarks) have been established throughout Canada based on conventional levelling whose observations date back to 1904. There are approximately 80,000 benchmarks over 120,000 kilometres of levelling lines.

The values were revised in: 1931; 1963; 1965; 1971; 1978 and 1980. In 1988 unexplained discrepancies of the order of 1.5 metres hindered an adjustment being implemented.

The geodetic datum in place does not represent today's required accuracy and the responsible Federal Agency acknowledges that there are distortions of up to one metre.