Vertical Benchmarks
Over the past one hundred years, a national network of vertical control points or "benchmarks" was created by levelling along major roads and railways in Canada and by linking more than 30 tide gauges operated by Fisheries and Oceans Canada.
A benchmark and a levelling crew
The Canadian Geodetic Vertical Datum of 1928 (CGVD28) was realized in 1928 by doing a national scale adjustment of all levelling at the time. Since then new levelling was added and adjusted to the old in a piece-meal approach that inherently left distortions throughout the network.
The CGVD28 Primary Vertical Network
NRCan no longer expand nor maintain the CGVD28 network of benchmarks however CGVD28 is still to this day the official reference surface for heights in Canada.
Orthometric heights and full benchmark descriptions are accessible via the CSRS Online Database. You can also download coordinates (but no description) of CGVD28 benchmarks from Geobase (as GML or shapefile) under "PRIMARY VERTICAL BENCHMARKS CANADA LEVEL 1".
Levelling is costly and laborious (compared to GPS) but it still remains the preferred method for measuring height differences over short distances with the highest accuracy.
A new approach for measuring orthometric (or Mean-Sea-level) heights and height differences using GPS and a Geoid Model is being communicated and promoted through the Height Modernization Project.