Interpretation of the accuracy map

The results were then interpolated by weighted means, mainly using data supplied by the Cantons which was generated in the process of establishing the transformation network.
The accuracy map was produced from this data as follows:

• A 500 m grid was constructed covering the whole of Switzerland.
• For each grid cell a mean value for the accuracy was computed from the five nearest neighbouring points, up to a maximum distance of 1.5 km from the centre of each cell. The weight of each point was taken as inversely proportional to its distance from the centre (1/distance²).

The quality of the interpolation procedure depends both on the distribution and measurement accuracy of the check points and also on these points being as representative as possible. Although all of the data has been checked by swisstopo, in some cases it is possible that local discrepancies may arise in relation to existing geographical data such as points of detail or boundary points. swisstopo therefore cannot guarantee the accuracy in this respect. In addition the positioning accuracy using global navigation satellite systems (GNSS) depends on the satellite constellation so this must also be taken into account. Please also note that the accuracy map should not be used in conjunction with approximate local solutions such as CSCS (country specific coordinate system).

In capturing data for geographical information systems (GIS) such as utilities asset registers or plant records, swisstopo recommends the use of the swipos positioning service in the official reference system of the Canton in question. Currently only Valais Canton is operating in LV95 and all other Cantons still use LV03. Before any observing campaign the configuration of the satellite constellation should be analysed and if LV03 is to be used the accuracy of the transformation should also be checked using the FINELTRA data viewer. In general it is recommended to set up the GNSS receiver at a known control point, available online using the FPDS data viewer (control point data service), at the start of the observing campaign and again in the middle and at the end, in order to check the configuration and – in the case of LV03 – the transformation accuracy by means of the difference between the observed and the official coordinates. If this is not satisfactory it may be necessary to adjust the coordinates so as to achieve a local fit. A detailed decision tree for the survey of points of detail using swipos can be found on p. 6 of swipos news (April 2006).

(with high accuracy and reliability requirements, for example for the «ownership» layer)

The accuracy indicated by the FINELTRA data viewer is sufficient for many applications in geomatics. However, in some Cantons and regions, the accuracy displayed may not in fact be achieved owing to deformations in the local data or where subsidence or landslips have continued over a period. Thus the accuracy of individual points cannot be deduced from the FINELTRA data viewer. For official cadastral survey applications it is essential to carry out a local adjustment, if only to demonstrate that it is not in fact necessary (see the directive for the application of GPS). Obviously the provisions of the Technical Ordinance on Official Cadastral Surveying (SR 211.432.21), especially with regard to accuracy requirements, remain in force and must be applied.