xkcd.WTF!?

Explanation ➲

Cueball and Megan have found a survey marker on the ground. Survey markers such as these are used as reference points for the NAD 83 and NAVD 88 geodetic reference systems, and the U.S. National Geodetic Survey has a database storing the coordinates of these markers. However, those two systems are being replaced by the New Datums of 2022 (delayed to 2025-2026), which is primarily based on satellite systems and gravimetric models.

When they update the database in the comic, Cueball's position, both horizontal and vertical, changes to compensate, leaving him panicking in mid-air. In reality, updating a database to change the coordinates of a location would not physically move items at the location.^{[citation needed]} Arguably, if they did, no one would notice much, since everything surrounding them should similarly move simultaneously to its corrected position as well. On the other hand, if the markers were updated and moved relative to each other, and (as the comic suggests) items shifted based to match the new markers, this could mean that objects would be stretched or compressed depending on whether the new markers were closer or further away from each other from their previous positions. However, in the comic, the only things whose position is 'known' (and can therefore be 'corrected') are those that are directly on a marker, hence why this shifting does not seem to apply to Megan (or her phone).

The title text refers to NAD 83 being around 7 feet off. This probably refers to the difference of about 7.2 feet (2.2 m) in the positioning of the centers of the notional Earth ellipsoids used as the basis for NAD 83 and WGS 84. This is also one of Randall's fun facts.

Absurd outcomes from differing survey standards was also the topic of 2888: US Survey Foot.