What counts as
a high reading?

Two ways to write the same thing

Ambient radio-frequency exposure is usually written either as power density (S, in W/m² or µW/m²) or as electric field strength (E, in V/m). For a single plane wave in the far field they are locked together by the impedance of free space:

S = E² / 377   ·   µW/m² = E² × 2 652

µW/m² means microwatts — millionths of a watt — per square metre. 0.04 W/m² is 40 000 µW/m², not 40 milliwatts: the unit describes a power per area, not a total power.

The limits that actually apply in Switzerland

Swiss law (the NISV ordinance) uses two different values, and they are ten times apart:

• Installation limit value (Anlagegrenzwert, 4–6 V/m depending on frequency): the binding value for each individual mobile installation, applied where people stay regularly — dwellings, schools, hospitals, offices.
• Immission limit value (Immissionsgrenzwert, derived from the international ICNIRP reference levels, roughly 40–61 V/m in the mobile bands): the value for the total exposure from all sources at any place where people may stay.

The installation limit is what makes the Swiss approach precautionary by international standards: it is up to ten times lower than the immission limit, and each installation is judged on its own rather than on the sum.

What is actually measured in Switzerland

The federal government measures exposure itself. In the third national measurement report (published May 2025), the highest single value recorded anywhere was 0.48 V/m at an airport, and the medians were 0.08 V/m at schools and 0.09 V/m at village centres. Converted, that is roughly 610 µW/m² at the very top of the distribution and about 20 µW/m² at a typical village centre — far below every limit in the tables above.

How this map's numbers compare with those

This map does not measure anything. It calculates an upper bound from the power class BAKOM registers for each installation. Each mast is given a path-loss profile that never attenuates less than free space, so the figure is bounded by the free-space one, and the model deliberately contains none of the things that reduce real exposure.

How far out can one figure be? Roughly a factor of two — treat any single number here as "of the order of", never as a reading. That is not one error term but several, and they pull in different directions. The power class is a permitted maximum rather than what the site transmits, which is the largest single factor and always pushes the figure up. The mast height, the down-tilt and the vertical beam are three nationwide constants standing in for per-installation values, and a real installation can sit above or below all three — a site tilted far down puts more of its power into the ground near itself than the model assumes, one tilted barely at all puts less. And the vertical pattern is a single idealised shape for every panel in the country. Three of those biases run upward, which is why the result is an envelope overall, but the tilt and height assumptions can move an individual site's ground-level figure in either direction. So the useful content of the map is the comparison — which places are higher, which sectors face where, and by roughly how much — and the absolute figures are offered at about the precision a factor of two allows.

Taken over the 2,123 municipality centres — the inhabited point of each, which is what the settlement table leads with — the modelled field, under the shipped automatic model, has a median of about 0.2 V/m: two to three times the measured village medians above, and still below the highest single value that programme has ever recorded. The busiest town centres read in the mW/m² range: the model puts the densest city squares at 1.7–3 V/m, and the very busiest — a main station forecourt, a stadium — higher again. Most centres read below the 200 µW/m² shipped threshold — so the exposure layer is dark over most of the country, amber where the installations are dense, and empty altogether in the Alps and on the passes. Those figures are to be read as an envelope rather than an estimate: the same places measure well under 0.5 V/m in the federal programme.

That gap is not a calculation error. It is the sum of what the model leaves out or has to assume, each item of which only ever adds:

• Class power, not operating power. The inventory gives a power class — up to 6 W, 500 W, 5 000 W, or more than 5 000 W — and the model uses the top of the class. An installation is normally configured well below its permitted maximum, and its actual output at any moment depends on traffic.
• A vertical pattern built from nationwide constants. The beam is tilted below the horizon and its gain does fall away above and below that axis, so the beam's axis meets the ground about 140 m out at the assumed 16 m mast height, the modelled field is strongest near 85 m where that gain and the falling path term balance, and the ground directly beneath a mast is a weak position, as measurement finds. What no public file carries is the real mast height, down-tilt, vertical beamwidth or panel pattern, which are per-installation values: one set of constants (16 m, 6°, 10°) therefore stands for every mast in the country, and a real installation may be above or below them.
• No buildings, terrain or vegetation. Walls cost 10–20 dB or more, ground clutter and hills cost more. None of it is here.
• Everything transmits at once, at full power. Every installation whose own fan covers the point is added together as if all of them were at their maximum simultaneously — 101 masts stand within 500 m of Zurich main station and 7 of their own contours cover the point; at the Wankdorf stadium the same two figures are 31 and 4. A place where nothing covers it reads below the threshold instead: a summit or a ridge in the Alps reads essentially zero here, which is what the map shows there.
• One cut-off, shared by the colours and the numbers. A mast contributes only out to three times its own contour radius, because that is as far as the map draws it. Past that the contribution is small — an eleventh of the threshold or less from any single installation — but there are thousands of installations, and summing their tails regardless was what once made a village with no fan over it read twice the threshold while the map showed it as quiet. The figure you read under the pointer is now the same quantity that is painted under it, which is a cut-off you can check by eye and a lower bound on the true sum.

So read the map as a comparison, not as a measurement: it is good at showing where exposure is higher or lower, which direction a sector faces and how close the nearest installations are. The absolute figures are an envelope that reality sits well below — by a factor of roughly two to three at the median centre and by an order of magnitude where the model is loudest — and they should not be read to better than about a factor of two either way. Two numbers worth keeping in mind: the shipped threshold is 200 µW/m², or 0.27 V/m, a little above the modelled median centre; and 500 µW/m² (0.43 V/m) is just under the highest value the federal measurement programme has ever recorded anywhere in Switzerland.

Is the ordering right? Named places, checked

A model can be too high everywhere and still be useless. What matters is whether it puts the right places in the right order and by a defensible margin, so the summed estimate is sampled at ten named locations by the verification harness, at the same 25 m reference distance the rest of the map uses. Every figure below is a worst case on the model's own assumptions, not a measurement:

• Matterhorn summit 0.00 V/m, middle of Lake Lucerne 0.00 V/m, Jura ridge 0.00 V/m — the three places in the sample with no installation within a kilometre. All three read zero at the shipped settings: the summit and the lake because no installation's own contour reaches them, and the ridge because its nearest mast is 1.4 km away and the summed field is not carried that far. These are figures for the map as it opens — the reach of the sum follows the threshold and the model — so they are quoted at the shipped default rather than as properties of the place.
• Grimsel pass 0.33 V/m and Vals village centre 0.75 V/m — a high pass with a handful of masts, and a 1,000-resident alpine village. The village reads several times the measured village-centre median, which is the envelope this model is built to be.
• Glarus town centre 0.66 V/m, Wankdorf stadium, Bern 0.80 V/m, Basel Marktplatz 1.58 V/m, Zurich main station 1.44 V/m, Zurich Bellevue 2.95 V/m — the densest places, where dozens or hundreds of sectors stand within a few hundred metres of the sample point and the sum is at its loudest. Nothing here is a measurement; the measured maximum anywhere in Switzerland is 0.48 V/m.

The ordering is what a reader would expect from the inventory and from the published measurements: open ground lowest, a village in the middle, dense towns highest, with the model's over-estimate growing exactly where the assumptions bite hardest — many overlapping installations, all assumed to transmit at their permitted maximum at once, with no buildings in the way. The harness prints the full table, including how many masts stand within 500 m of each point and how many of their contours cover it, so the figures can be traced back to the inventory rather than taken on trust.

Fans, or the summed field

One view draws one fan per antenna, and a fan is that installation's own threshold contour: its edge is where that mast alone falls below the level. That is the readable view, and it is deliberately not the quantity a person at a point is exposed to. Two masts that each deliver 300 µW/m² show two fans that stop short of a 500 µW/m² line while the ground between them is over it, because the field is a sum.

Combined field — the view the map opens in — is that sum: the same model evaluated once per pixel with every mast added, painted from the summed value and bounded by the summed field's own contour, drawn as a single black line. Measured at Zurich at zoom 11 and the default 200 µW/m² signal threshold — the same control the fan view uses, so the two are directly comparable — the summed region covers 44% of the view against the 26% the fans cover, and 41% of it is ground that no fan reaches — the part that only exists because contributions add. It is the heavier view, and the raster is sampled more coarsely to keep the frame inside the same budget — the price of it being the shipped default, since it is the quantity the readouts report. The sum is accumulated out to three times each fan's radius; past that a mast contributes an eleventh of the threshold or less, so the view slightly under-states the field in open country, which is the safe direction for the one number on this site that people act on.

The low-exposure disks are drawn one per settled place — every OpenStreetMap place node in Switzerland with a settlement class, 15,174 of them: 10 cities, 166 towns, 3,502 villages, 6,839 hamlets and 4,657 isolated dwellings (single farmsteads, the quietest addresses in the country) — and each one's radius is the distance from that place to the nearest ground the map paints above the threshold, so a rim is tangent to the coloured region on screen and none is drawn over ground the map has already coloured. The two views get that distance differently, and the difference is the reason it can be checked with a ruler. In the per-mast view the boundary is a fan contour the model solved, and the distance to it has a closed form: exact, at any zoom, and independent of what happens to be on screen. In the combined view the boundary is the summed field's own contour — which depends on every mast at once and has no closed form — so there it is read off the raster that was just painted, and a place whose nearest contour lies outside the frame has no disk at that zoom. A place the map already colours gets no disk in either view, which is the honest answer rather than a missing one. Measuring the remaining places is about a second of arithmetic, worked through in slices rather than in one call, so a threshold change never freezes the map — the layer fills in over roughly a second and nothing is recomputed while panning or zooming. Where two disks overlap they are filled as one union, so the shared ground takes the same tint rather than doubling it, and neither rim is drawn across the other's fill: that overlap is not a boundary the model measured. The settlement's name is redrawn over the wash in the tile's own style and at its own coordinate, because a translucent wash over a place label is exactly what makes the name unreadable. The layer can also be drawn the other way round — Everywhere washes every area below the threshold in green instead of drawing one disk per place. It trades the checkable rim for covering the whole country at once, including the places whose nearest contour lies outside the current frame and the ones whose rim would have nothing on screen to land on; it is the complement of the amber by construction, so no pixel is ever both, and it has no rims to click.

How the published guidance levels compare

Below about 2 GHz the international reference level falls with frequency, so at 900 MHz the ICNIRP value is about 4.5 W/m² (≈41 V/m) rather than 10 W/m². That is why Swiss and German limit tables list different numbers for different bands.

Do other countries allow less?

Some do, and the comparison is easy to get wrong. National limits differ not only in value but in definition: per installation or summed across all operators, averaged over six minutes or over a day, at a fixed frequency or across a band, at places of sensitive use or everywhere people may be. A single number taken from another country is therefore not directly comparable with the Swiss installation limit, which applies to one installation at a time at sensitive locations.

What can be said precisely: the Swiss installation limit is roughly ten times stricter than the Swiss immission limit, and the immission limit follows the international ICNIRP reference levels. Several countries and regions have adopted precautionary values in the same range as the Swiss installation limit or below it, and several have no additional precautionary value at all. The regulatory structure varies as well — Belgium, for instance, regulates per region (Flanders, Wallonia and Brussels) rather than nationally.

For any specific country, use the current rule published by the responsible authority, and check which definition it uses before comparing it with the figures above. For the separate question of how easily a community can keep an installation out, see Radioguard — how strict a limit is and whether a village can refuse an installation are two different things.

What measurements usually find

Federal and cantonal measurement programmes in Switzerland repeatedly report ambient outdoor values far below the limits. Published medians for dwellings and schools typically fall in the range of roughly 0.02 to 0.1 V/m (about 1 to 30 µW/m²), with the highest single values in dense city centres or close to an airport in the range of a few tenths of a volt per metre. In other words: most measured places sit below even the strictest precautionary proposals, while individual spots in a main beam can exceed them.

Why the map shows bigger numbers than that

The shaded field on this map is an upper bound rather than a prediction. It adds the permitted maximum power of every nearby sector, in the direction of the point, with no buildings, no terrain, no vegetation and no allowance for the fact that a network almost never transmits at full power. That makes it useful for comparing places and directions, and unsuitable for reading as a measured value. Use the numbers from the panel and the popups to rank what is near you, not as an absolute exposure figure.

The vertical pattern is modelled, and it is what makes the numbers near the ground behave. A macro panel stands tens of metres up and is aimed at or slightly below the horizon, so its beam is only about 7–10° tall, and a person on the ground fifty metres out sits 10–30° below that beam, where a real panel radiates twenty decibels or more below its maximum. The model therefore assumes a 16 m mast, a 6° down-tilt and a 10° vertical beam, which puts its strongest ground ring about 140 m out and makes the ground directly under a mast a weak position rather than the strongest one. What it cannot carry — because no public file publishes them — are the real height, tilt, vertical beamwidth and panel pattern, which differ from installation to installation. Figures very close to a mast are still the least reliable on the map, so a large reading should be read as the top of a wide range rather than as an estimate. The permissioned BAKOM sector export would replace those three constants with each installation's own values.