Editing 2920: Survey Marker

Jump to: navigation, search

Warning: You are not logged in. Your IP address will be publicly visible if you make any edits. If you log in or create an account, your edits will be attributed to your username, along with other benefits.

The edit can be undone. Please check the comparison below to verify that this is what you want to do, and then save the changes below to finish undoing the edit.
Latest revision Your text
Line 10: Line 10:
  
 
==Explanation==
 
==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.
+
{{incomplete|Created by a GUIDED MISSILE THAT MISSED THE TARGET DUE TO COORDINATE DRIFT - Please change this comment when editing this page. Do NOT delete this tag too soon.}}
 +
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 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 off of 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).
+
When they update the database, in the comic Cueball's position changes to compensate. In reality, updating a database to change the coordinates of a location would not physically move items at the location.{{cn}}
  
−
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]].
+
The title text refers to NAD 83 being around 7 feet off. This is in reference to both WGS84 and presumably the New Datum.
−
 
 
−
Absurd outcomes from differing survey standards was also the topic of [[2888: US Survey Foot]].
 
  
 
==Transcript==
 
==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.]
 
:[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  
+
:U.S. Geological survey bench mark  
 
:Elevation above sea 447 feet
 
:Elevation above sea 447 feet
 
:Cueball (off-panel): I love finding these survey markers. It's somehow reassuring.
 
: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 and Megan are show 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: I like that someone, somewhere, knows where this spot is.
 
:Cueball: If I stand on it, they know where '''''I''''' am.
 
:Cueball: If I stand on it, they know where '''''I''''' am.
  
−
:[Cueball and Megan look up at each other.]
+
:[Cueball and Megan looks 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: 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 is looking down at her phone in her hand, standing in the same relation to the marker. But Cueball is now floating in the air behind her 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.
 
:Megan: Oh look, it just got updated.
 
:Cueball: '''''Hey! Put me back!'''''
 
:Cueball: '''''Hey! Put me back!'''''
Line 40: Line 39:
 
[[Category:Comics featuring Megan]]
 
[[Category:Comics featuring Megan]]
 
[[Category:Geography]]
 
[[Category:Geography]]
−
[[Category:Fun fact]]
 

Please note that all contributions to explain xkcd may be edited, altered, or removed by other contributors. If you do not want your writing to be edited mercilessly, then do not submit it here.
You are also promising us that you wrote this yourself, or copied it from a public domain or similar free resource (see explain xkcd:Copyrights for details). Do not submit copyrighted work without permission!

To protect the wiki against automated edit spam, we kindly ask you to solve the following CAPTCHA:

Cancel | Editing help (opens in new window)

Templates used on this page:

Retrieved from "https://www.explainxkcd.com/wiki/index.php/2920:_Survey_Marker"