Editing 2920: Survey Marker

{{comic
| number    = 2920
| date      = April 15, 2024
| title     = Survey Marker
| image     = survey_marker_2x.png
| imagesize = 740x272px
| noexpand  = true
| titletext = Fun fact: The standard North American NAD83 coordinate system is misaligned from the actual Earth, off-center by about 7 feet. Someone knows where I am, and I'm in the wrong place.
}}

==Explanation==
Cueball and Megan have found a {{w|survey marker}} on the ground. Survey markers such as these are used as reference points for the {{w|North American Datum|NAD 83 and NAVD 88}} geodetic reference systems, and the {{w|U.S. National Geodetic Survey}} has a database storing the coordinates of these markers. However, those two systems are being replaced by the {{w|National Spatial Reference System#Datum of 2022|New Datums of 2022}} (delayed to 2024-2025), 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 {{w|North American Datum#Comparing NAD 83 to WGS 84|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 {{w|World Geodetic System|WGS 84}}. This is also one of [[Randall]]'s [[:Category:Fun fact|fun facts]].

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

==Transcript==
:[Zoomed in view of a round marker on the ground, with small specks of dirt around it. There is one line of text going around the central part in the outer rim of the marker, with the first three words written around the top, and the last two words written around the bottom (thus not text that are going all the way around in one single line). Inside this rim there are more text on three lines. In the center there is a small cross in a triangle pointing up in relation to the central text. There are more unreadable text below the last line of text and around the inner part of the rim. And off panel voice, which in the next panel turns out to be Cueball, is written above the mark.]
:U.S. Geological survey bench mark 
:Elevation above sea 447 feet
:Cueball (off-panel): I love finding these survey markers. It's somehow reassuring.

:[Cueball and Megan are shown as they look down on the marker. Cueball has one leg on either side of the marker and Megan stands to the right.] 
:Cueball: I like that someone, somewhere, knows where this spot is.
:Cueball: If I stand on it, they know where '''''I''''' am.

:[Cueball and Megan look up at each other.]
:Megan: But the NAD83 and NAVD88 datums are getting replaced soon. That marker's coordinates could shift by like 5 feet.

:[Megan is looking down at her phone in her hand, standing in the same place in relation to the marker. Cueball is now floating in the air behind her about 5 feet above the ground, while flailing with his arms and legs (as shown with three small curved lines at the end of either arm and above and below him).]
:Megan: Oh look, it just got updated.
:Cueball: '''''Hey! Put me back!'''''

{{comic discussion}}

[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Megan]]
[[Category:Geography]]
[[Category:Fun fact]]