Concepts and definitions
WGS84 is a global coordinate system developed by the US Department of Defence. WGS84 is used in navigation systems such as GPS (since 1987). It is time-dependent and thus not suitable as a basis for charts. However, the accuracy is sufficient for navigation in practice.
EUREF 89 is a pan-European coordinate system, which is identical to the WGS84 down to an accuracy of one metre. It is fixed to the Eurasian continental plate and is not time-dependent.
EUREF-FIN is the Finnish realisation of the above (national densification).
KKJ, a grid coordinate system, is the national coordinate system used in Finland. The system uses the Hayford ellipsoid as the reference ellipsoid.
Blue nautical charts (since 2003)
The coordinate system EUREF-FIN used for the blue nautical charts is based on the coordinate system WGS84, which is compliant with international maritime standards. WGS84 is also used in the GPS satellite system. The difference in coordinates using WGS84 and EUREF89 is less than one metre, so seafarers do not have to take the negligible difference into account when navigating.
Green nautical charts
The coordinate system used in Finnish nautical charts is based on the national grid coordinate system KKJ. The reference ellipsoid used is the international reference ellipsoid INT 1924 (Hayford 1910). The coordinate system WGS84 used in GPS satellite positioning equipment differs from the Finnish system. The approximate differences between the coordinate systems KKJ and WGS84 are described with examples in the table below.