No country that I know of uses one of the WGS84 frames for their official datum, and IMO they'd be crazy to do so if they cared about regional accuracy and stab

No country that I know of uses one of the WGS84 frames for their official datum, and IMO they'd be crazy to do so if they cared about regional accuracy and stability of the frame, and having some kind of say in how it's realized. The reason I say this is that the WGS84 frame is maintained by the NGA (US National Geospatial Intelligence Agency) based on a relatively sparse and worldwide GPS base station network, and updated to a new version whenever they deem necessary. (So far we're up to the sixth version of the frame, officially known as "WGS 84 (G1762)" - see http://earth-info.nga.mil/GandG/publications/NGA_STND_0036_1_0_0_WGS84/NGA.STND.0036_1.0.0_WGS84.pdf http://earth-info.nga.mil/GandG/publications/NGA_STND_0036_1... for the gory details) Note that "using the (current) WGS84 datum" is a very different thing from "using GPS measurements to define a national datum". At the most basic level, GPS measurements just give you timing information which allow you to work out how far you are from the current set of visible satellites. However, to figure out where you are in some well defined coordinate system, you also need the position of the satellites themselves as a function of time (their /ephemerides/, in the jargon). But wait, there are no absolute physical reference frames, so the positions of the satellites themselves need to be measured with respect to something. This "something" is generally a network of GPS base stations attached to the ground in geophysically stable locations. Depending on which set of ground stations you choose and your processing conventions, you'll compute different ephemerides for the satellites. The NGA have one such set of base stations, and they use it to compute the WGS84 /broadcast ephemerides/ which are broadcast by GPS satellites every 30 seconds. But you can make your own! For example the IGS (International GNSS Service, ugh, acronyms) use a much denser set of base stations all around the world to compute their own ephemerides, giving datum IGS14 (previously IGS08) and I believe there's a public transparent process for nations to contribute to this frame. So if you want to define a stable and accurate national datum using GPS measurements, I believe the procedure goes something like this: 1) Build a robust set of GPS ground stations, well distributed across the land mass 2) Observe GPS timing signals continuously at all base stations 3) Solve for the positions and velocities of the base stations to realize a terrestrial reference frame defined by your base stations. Some arbitrary but conventional choices must be made here - for example, what's the orientation of the cartesian coordinate axes? 4) Process the GPS observations each day/week/whatever, along with a (potentially less dense) set of measurements contributed by the rest of the world to compute satellite ephemerides. 5) Make the resulting ephemerides publicly available, so people can realize high precision measurements in your datum, by combining with their own GPS measurements. tl;dr - All measurement is relative. The GPS satellite constellation is used to transfer a coordinate frame defined by some ground control stations (you pick which ones!) back to any other point on the ground. [edit - formatting]