<p>I've downloaded the csv files for <a href="https://vizier.cds.unistra.fr/viz-bin/VizieR-3?-source=V/154&amp;-out.max=50&amp;-out.form=HTML%20Table&amp;-out.add=_r&amp;-out.add=_RAJ,_DEJ&amp;-sort=_r&amp;-oc.form=sexa" rel="nofollow noreferrer">SDSS DR16</a> and <a href="https://vizier.cds.unistra.fr/viz-bin/VizieR-3?-source=VII/289&amp;-out.max=50&amp;-out.form=HTML%20Table&amp;-out.add=_r&amp;-out.add=_RAJ,_DEJ&amp;-sort=_r&amp;-oc.form=sexa" rel="nofollow noreferrer">DR16Q</a> and made a map of their sky distributions:</p>
<p><a href="https://i.sstatic.net/3nMZW.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/3nMZW.png" alt="enter image description here" /></a></p>
<p>The coordinates come from:</p>
<ul>
<li>DR16: <code>RA_ICRS</code> and <code>DE_ICRS</code></li>
<li>DR16Q: <code>RAJ2000</code> and <code>DEJ2000</code></li>
</ul>
<p>Why do they overlap only partly? Isn't DR16Q a subset of DR16?</p>

CC BY-SA 4.0
2022-06-22T03:30:46.117Z
Stupid question but have you checked you're getting the full catalog or subsampling the complete catalog (every 100th row or something throughout the full dataset) ? If the two catalog's rows are arranged differently, then if you have a hit a row limit in the extraction, you would get different sky coverage... just a thought
astrosnapper
CC BY-SA 4.0
2022-06-22T04:05:44.540Z
@astrosnapper I thought of that, but I'm pretty sure I downloaded the files using the default settings from VizieR, and I've checked; they seem to be the full samples.
Jim421616
<coordinate><sky-survey>
Why are the sky distributions of SDSS DR16 and DR16Q different?
Jim421616
# Why are the sky distributions of SDSS DR16 and DR16Q different?

(Asked by: username_0 on 2022-06-20)

I've downloaded the csv files for [SDSS DR16](https://vizier.cds.unistra.fr/viz-bin/VizieR-3?-source=V/154&-out.max=50&-out.form=HTML%20Table&-out.add=_r&-out.add=_RAJ,_DEJ&-sort=_r&-oc.form=sexa) and [DR16Q](https://vizier.cds.unistra.fr/viz-bin/VizieR-3?-source=VII/289&-out.max=50&-out.form=HTML%20Table&-out.add=_r&-out.add=_RAJ,_DEJ&-sort=_r&-oc.form=sexa) and made a map of their sky distributions:

[![enter image description here](https://i.sstatic.net/3nMZW.png)](https://i.sstatic.net/3nMZW.png)

The coordinates come from:

* DR16: `RA_ICRS` and `DE_ICRS`
* DR16Q: `RAJ2000` and `DEJ2000`

Why do they overlap only partly? Isn't DR16Q a subset of DR16?

**Tags:** coordinate, sky-survey
> **Comments:**
> **username_1**: Stupid question but have you checked you're getting the full catalog or subsampling the complete catalog (every 100th row or something throughout the full dataset) ? If the two catalog's rows are arranged differently, then if you have a hit a row limit in the extraction, you would get different sky coverage... just a thought  
> **username_0**: @astrosnapper I thought of that, but I'm pretty sure I downloaded the files using the default settings from VizieR, and I've checked; they seem to be the full samples.  

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## 0 answers

