Layers 0
Every layer in the app. A category shows its own layers while you are in it; pin one and it stays on wherever you go.
Constellations
Orbital elements are fetched once and propagated in your browser, so nothing streams while you watch. The number beside each name is how many of its satellites are in orbit today, counted from the catalogue; switching one on draws the objects CelesTrak tracks for it, which for GPS is the operational set rather than every NAVSTAR still up there.
Vehicle type
Everything is drawn; switch one off to take it off the map.
Air layers
Air quality is the US EPA index, from the Copernicus CAMS global forecast, reported at cities rather than on a grid — because air quality is something that happens to people. Pollen is modelled over Europe only; elsewhere it reports none rather than zero.
Minimum index
The layer asks about the cities on screen, biggest first, up to two hundred at a time. Zoom in for the smaller ones.
Ship type
Everything is drawn; switch one off to take it off the map. A ship's type arrives with its static report, every six minutes, so freshly seen ships start as "not reported".
Earth layers
Earthquakes are every M2.5+ event USGS has listed in the last 24 hours. Volcanoes are the eruptions the Smithsonian has not yet closed, this week’s observatory reports, and the US alert levels — over the 1,214 volcanoes that have erupted since the last ice age.
Volcanoes shown
Minimum magnitude
USGS lists every M2.5+ event worldwide within minutes. Below M4 the map fills with the constant background of small quakes; the Stats list follows this threshold too.
Operators
Each operator publishes where it runs; this is those lists on one map. A dot is a place, not a building: a cloud region is several data centres a few miles apart, a colocation metro is a dozen buildings under one brand, and a campus is one site.
Every mark is a hail report the Storm Prediction Center collected today, with the stone size somebody measured or compared to a coin — not a model's guess that conditions looked right. The mark grows with the stone. United States only: the SPC publishes for its own country and no equivalent open feed covers the rest of the world.
Freezing rain does its damage before anyone sees it arrive, so this shows warnings rather than observations: an Ice Storm Warning, a Freezing Rain Advisory, or a Winter Storm Warning whose text is about ice rather than snow. A mark means the National Weather Service has that warning in force now. United States only.
Aerosol optical depth is how much of the sky's light the air takes out. Wildfire smoke is what usually raises it — a plume off a fire front can carry a thousand miles and turn the daylight orange under it — but dense haze over a city and a dust outbreak do the same, which is why this layer is named for what it measures rather than claiming to know what is burning. The dust layer separates that part out. Clean air is not drawn.
Mineral dust lifted off deserts and dry lake beds, from the Copernicus CAMS forecast. A dusty afternoon is tens of micrograms a cubic metre; a Saharan outbreak crossing the Atlantic or a haboob rolling off the Sahel runs into the thousands. Air with little dust in it is not drawn.
A shower is the Earth ploughing through the dust a comet left along its orbit. The marker sits where the radiant — the direction the meteors come from — is directly overhead, which sweeps west at fifteen degrees an hour as the planet turns. Inside the dashed ring the radiant stands at least twenty degrees up, which is the difference between a shower worth going outside for and one below the horizon.
Minimum face height
Minimum quality
Water temperature
Defaults: 3 ft faces and Fair or better, which is what most people would paddle out for. Quality is a call from swell exposure, peak period and wind against each break's facing; nothing selected under water temperature means every band is shown.
Space layers
Satellites are propagated locally from their orbital elements; the aurora is NOAA’s OVATION model. Both are the sky above you, so they share a mode.
Minimum chance
NOAA’s OVATION model gives the chance of seeing aurora overhead in the next half hour, for every degree of the globe. Below about 5% the model is saying “no” rather than “faint”.
Hemisphere
Weather layers
Storms are tropical cyclones with an advisory in force (NHC, JTWC). Rain and snow are every 0.25° cell where the GFS weather model says it is falling this hour. Sunshine is assumed everywhere else.
Jet Stream floor
The jet streams are the wind at about 34,000 feet — the level airliners cruise at. Sixty knots is the conventional threshold for calling it a jet stream at all.
Rain intensity
Bands are rainfall rate (WMO): light under 2.5 mm/h (0.1 in/h), moderate to 7.6 mm/h (0.3 in/h), heavy to 50 mm/h (2 in/h), violent above. Cells under 0.2 mm/h — a trace — are left out.
Snow intensity
Bands are snowfall rate: flurries under 0.1 in/h (0.25 cm/h), light to 0.5 in/h, moderate to 1 in/h, heavy above that. The rate is the model's liquid precipitation times a snow-to-liquid ratio that follows temperature (10:1 near freezing, more in colder air).
Clouds
Total cloud cover from the same GFS hour, to the nearest 5 %, drawn under the rain and snow wherever at least 30 % of the sky is covered. Off by default, so the map is not blanketed. The three chips beside Clouds switch the types: partly cloudy to 60 %, mostly cloudy to 85 %, overcast from 90 % — switch Overcast off to lift the solid deck and keep the thin cloud. Land only hides clouds over the sea too.
Floods
Flooding in force: every flash flood, river flood, coastal flood and storm surge alert the US National Weather Service has out, the river gauges standing at or above their action stage, and the flood events GDACS is tracking worldwide. Areas are the alert's own outline where it has one, otherwise the zones it names. On by default.
Wind
The sustained wind at ten metres from the same GFS hour — the wind that keeps blowing, not gusts, which run higher and are not drawn. Over land and sea alike, nothing in the sky. On by default, drawn from 20 mph up unless you raise the floor. Arrows point the way the wind blows and are coloured by Beaufort band.
Rain over the tropical oceans and snow over polar sea ice are most of the area. The Stats lists follow these filters.
Aircraft colour
Category
Everything is drawn; switch one off to take it off the map.