There have been (oil) wells fail because someone gave a lat/long without specifying the datum, and someone else assumed it was in a different datum.
Without a datum defined, latitude/longitude (no matter how precise) only gets you to within ~1km of an actual location.
The Earth is not a sphere (or even an ellipsoid). Therefore, we need models of the the absolute shape of "sea level" (i.e. an equipotential surface - varies due to density variations in the Earth) to go from a spherical coordinate system to an actual point on the Earth's surface. These are referred to as a datum.
Because our knowledge of the absolute shape of the Earth has changed over time, there are many different datums (ranging from spheres to ellipsoids to detailed gridded surfaces).
There are a large number of datums that are still in common use. WGS84 is the most common (and very accurate), but NAD83 and NAD27 are also very, very common, as well as many others. If someone gives you a lat/long in NAD27 (e.g. read off of a printed map) and you assume it's WGS84, you can wind up over a kilometer away from the original location. (NAD27 is reasonably accurate for the US, but is very inaccurate elsewhere on the planet. I regularly see it used for data everywhere, though.)
You're absolutely right, and I should have said that!
I was trying to contrast to the case of just typing it into some kind of map service, i.e. MapCodes. A lat/long pair unambiguously resolves to a single point in that service.
This is a tangent, but actually, they're not.
There have been (oil) wells fail because someone gave a lat/long without specifying the datum, and someone else assumed it was in a different datum.
Without a datum defined, latitude/longitude (no matter how precise) only gets you to within ~1km of an actual location.
The Earth is not a sphere (or even an ellipsoid). Therefore, we need models of the the absolute shape of "sea level" (i.e. an equipotential surface - varies due to density variations in the Earth) to go from a spherical coordinate system to an actual point on the Earth's surface. These are referred to as a datum.
Because our knowledge of the absolute shape of the Earth has changed over time, there are many different datums (ranging from spheres to ellipsoids to detailed gridded surfaces).
There are a large number of datums that are still in common use. WGS84 is the most common (and very accurate), but NAD83 and NAD27 are also very, very common, as well as many others. If someone gives you a lat/long in NAD27 (e.g. read off of a printed map) and you assume it's WGS84, you can wind up over a kilometer away from the original location. (NAD27 is reasonably accurate for the US, but is very inaccurate elsewhere on the planet. I regularly see it used for data everywhere, though.)