Your current elevation, from the ground up
The brown sign shows the elevation of the ground at your position: how far the land surface is above mean sea level. For US locations it leads with feet and gives metres underneath; elsewhere it leads with metres.
The number does not come from your phone's altitude reading. It comes from a digital elevation model, a grid of measured ground heights built from aerial laser scans, radar and survey data. In the United States that grid is mostly the USGS 3D Elevation Program, with points roughly every 10 metres and closer in many places. When we checked a point in downtown Denver, the model gave 1,596.7 metres, against 1,596.4 metres from the USGS's own elevation query service.
Your phone's own GPS altitude, when it reports one, is shown separately in the rows below the signs. The two rarely match exactly, and that difference is worth understanding.
Why we show ground elevation instead of GPS altitude
Phone GPS is good at horizontal position and much weaker at height. Vertical error is typically one and a half to two times the horizontal error, so a phone that knows its position to 5 metres may be 10 metres or more out on height. Indoors it can be much worse.
There is also a reference problem. GPS measures height above a mathematical ellipsoid, not above sea level. The difference, called the geoid height, is around 30 metres across much of the United States. Some devices correct for it and some do not, so raw GPS altitude can be off by that much even with a perfect fix.
Ground elevation from a model has neither problem. It is also the number you want for most purposes: canning and baking adjustments, flood risk, hiking plans and property records all use the height of the ground. The GPS altitude versus elevation guide goes into the details.
If you are on the tenth floor of a building, the ground elevation is still the elevation of the street below. Add roughly 3 to 4 metres (10 to 13 feet) per floor if you need your own height.
What your elevation is useful for
- Home canning: water boils at a lower temperature as you go up, so processing times and pressures change above 1,000 feet. See elevation for canning.
- Baking: recipes start to need adjusting at around 3,000 feet. See high-altitude baking.
- Hiking and climbing: the effects of altitude begin to be noticeable for many people above about 8,000 feet.
- Flood risk: height above nearby water matters more than height above sea level, but both help when reading a flood map.
- Engines and sports: thinner air reduces engine power and changes how far a ball travels.
- Weather: air pressure readings are usually corrected to sea level, so you need your elevation to compare a barometer against the forecast.
How accurate the elevation is
In the United States, the underlying elevation data is generally accurate to within a metre or two on open ground. Two things make the reading less exact than that. First, the model is sampled on a grid about 5 metres wide at the zoom level we use, so on a steep slope or a cliff edge the value is an average for that cell. Second, the position itself is only as good as your device's fix.
Outside the US the model uses lower-resolution global data, typically with points about 30 metres apart, so expect accuracy of several metres. Over water the model shows the water surface or a sea-floor depth depending on the source, which is why a reading on a lake can look odd.
To check a different spot, tap the map. To check an address, type it in the search box, or use the elevation finder.