Jirí Polacek opened the following discussion topic in the main group, alerting about interoperability problems of commonly agreed state boders when they are provided by different members States:

https://themes.jrc.ec.europa.eu/discussion/view/21479/common-etrs89-coordinates-of-the-state-borders

Original description from Jirí:

Common unique ETRS89 coordinates of the state borders are not only taken for granted but also crucial for crossborder data harmonization.  Taking into account large scale map themes like Cadastral Parcels and Administrative Units, we can identify particular difficulties. From the point of view of data harmonization, cadastral parcels should fit the state border and the state border should contain the same ETRS89 coordinates from both neighbouring countries.

 This premise has been tested in the frame of the ELF project. Practical experience from the Czech-Polish cluster proved that none of these assumptions has been allways met. Discrepancies between parcels (derived from the cadastral maps) and state boundaries are usually caused by mistakes in the map and are easy to fix. On the other hand, if the state boundary is measured and administered in both national coordinate systems (this way is common for the international treaty on the state boundary), the accuracy of the transformation into the ETRS89 is influenced by discrepancies of the national trigonometric network, which results in two slightly different state boundaries in ETRS89. In case of the Czech and Polish boundary, the mean deviation was approximately 10 cm.

The only solution, which enables to fix the ETRS89 coordinates on the state boundary, lies within additional GPS measurements on  state borders. This approach guarantees the accurate official ETRS89 border coordinates, which should be approved by the international treaty.  This has been recently accomplished on the Czech-Slovak state border and is being prepared for the Czech-German and.

As view and download services for cadastral parcels and administrative units themes are being run in an on-line mode in the Czech republic, a special transformation is being prepared, which will convert the local Czech coordinate system JTSK to the ETRS89 as well as preserve fixed ETRS89 coordinates on the state border.

Since the discussion topic is related to Coordinate reference systems, please use this new discussion topic in the Coordinate reference systems subgroup for further discussion.

The topic is also a cross-cluster issue, at least overlapped with the Administrative units and the Cadastral parcels themes.

Feel free to participate!