🧭 Coordinates of San Francisco

San Francisco is at 37.77, -122.42 in WGS84 decimal degrees, which is 37° 46′ 12.0″ N, 122° 25′ 12.0″ W in degrees, minutes and seconds. It lies in the Northern and Western Hemisphere, 4,182 km from the equator along its meridian, 5,820 km from the nearest pole and 10,786 km from the prime meridian measured along its own parallel. Exchange the numbers in the form for any other position and the page reworks every one of them.

Reading San Francisco's position

Latitude runs from 0° at the equator to 90° at each pole and is written with the hemisphere letter or a sign — south is negative. Longitude runs from the prime meridian through Greenwich to ±180°, east positive. San Francisco at 37.77, -122.42 therefore sits 4,182 km of meridian arc from the equator and 10,786 km of parallel arc from Greenwich. The two numbers are not the same kind of distance: a degree of latitude is roughly constant (about 111 km, and the ellipsoid makes it 110.57 km at the equator, 111.69 km at the poles), while a degree of longitude shrinks with the cosine of the latitude, until it is nothing at all on poles. That is why this page gives the parallel distance separately instead of multiplying degrees by a single factor.

Why DMS, and what a GeoHash is for

Degrees-minutes-seconds is the format of charts, survey markers and aviation logs, because a minute of latitude is by definition close to one nautical mile. A GeoHash is something else entirely: it interleaves the longitude bits and latitude bits of a position and writes each group of five in a thirty-two symbol alphabet, so a cell that starts 9q8yy7 is a rectangle about 1.2 km by 0.6 km containing San Francisco. Two points that share a longer GeoHash prefix are near each other, which makes the string useful for indexing, grouping and typing a position into a map without entering two numbers.

The datum matters

Every figure here is WGS84, the same reference GPS broadcasts and web maps display. Older local datums (OSGB, Potsdam, and the various regional surveys) can put the same street corner hundreds of metres away on paper, so a coordinate quoted without its datum is incomplete. Conversions on this page touch no service: the meridian arc is Simpson integration of the exact WGS84 meridian integral, and the parallel radius comes from the ellipsoid's prime-vertical radius of curvature — both run in your browser, so the numbers are checkable and nothing you type leaves the device.

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