RIVM has updated the 2005 grid map (Netkaart) showing the overhead high-voltage lines in the Netherlands. The grid map has been modified because better data on the high-voltage grid is now available. The high-voltage grid has also changed in a number of places, for example because new high-voltage lines have been realised or existing lines have been brought underground, moved or taken down. The map is a tool for municipalities that need to decide on the design of the area near overhead high-voltage lines.

The grid map gives an indication of the width of the magnetic field zone along the overhead high-voltage lines. If new zoning plans are designed within this indicative zone, it is recommended to determine the zone for that specific location. In this 'specific magnetic field zone', the government recommends, for precautionary reasons, to prevent children from long-term exposure to an annual average magnetic field strength of more than 0.4 Microtesla, 'as far as reasonably possible'.

Grid operator TenneT has systematically recorded the data needed to calculate the specific magnetic field zone over the past five years. As a result, the data on the maximum flow of electricity through the lines, the locations of the masts and the way the cables hang in the masts are more accurate, reliable and traceable than before.

Due to the new data for the high-voltage lines, the indicative magnetic field zones of most lines have changed. In 62 percent of the lines, the zone has become narrower, and wider in 30 percent. In 8 percent of the lines, the zone has remained the same. Due to changes in TenneT's data, the specific magnetic field zones may also be different. This could be important for decisions about spatial planning near overhead high-voltage lines.

In the second half of 2018 the precautionary policy will be evaluated by the Ministry of Economic Affairs and Climate Policy - together with the Ministry of Infrastructure and Water Management, and the Ministry of the Interior and Kingdom Relations, municipalities, provinces and grid operators. This evaluation examines how the current precautionary policy affects implementation practice. The evaluation can lead to changes in the precautionary policy and as a consequence also in the modification of instruments such as the RIVM grid map with indicative magnetic field zones.