When zero is not always zero
The standard used until now – the mean sea level – was flawed from the outset: There was never a fixed definition. Every country could use arbitrary tide gauges to define its own zero level. As a result, Germany’s official sea level is 31 centimeters higher than Italy’s, 50 cm higher than that used in Spain and actually 2.33 m higher than in Belgium, where the zero height is based on low water in Ostend.
When topographical maps are only used for hiking, no one is bothered by such differences. But for geodetics specialists trying to arrive at a universally agreed height – for Mount Everest, for example, half in Nepal and half in China – the inconsistent zero levels are a bigger problem. And it can be very costly when planners of cross-border structures such as bridges and tunnels forget to check the different coordinates used by the teams and convert them as needed. On the Hochrheinbrücke, a bridge connecting Germany and Switzerland, a discrepancy of this kind was noticed just in time.
