# External galaxies (`data/galaxies/galaxies.bin`) — sources and terms

`data/galaxies/galaxies.bin` (44,213 galaxies, 1.5 MB) puts the known galaxies
beyond the Milky Way on the holo map (`scripts/galaxies.gd`). It is generated
by `tools/build_galaxies.py`, which downloads every source below (VizieR
`asu-tsv`, the CDS XMatch service, OpenNGC on GitHub) and can be rerun to
reproduce it. Downloads: 2026-09-28. How the sources are merged and which
distance wins: `docs/GALAXY.md`, "External galaxies".

The file is a compilation of published measurements and includes names, sizes,
axis ratios and position angles adapted from **OpenNGC** (CC BY-SA 4.0), so
Expanse distributes it under **Creative Commons Attribution-ShareAlike 4.0
(CC BY-SA 4.0)** — https://creativecommons.org/licenses/by-sa/4.0/ — the
licence of `data/deep_sky.csv`. Please keep the citations below, which the
catalogues ask for.

**VizieR.** This research has made use of the VizieR catalogue access tool,
CDS, Strasbourg, France (DOI 10.26093/cds/vizier); the original description of
the VizieR service was published in Ochsenbein, Bauer & Marcout 2000, A&AS 143,
23. Cross-matching used the CDS XMatch service (Boch et al. 2012, ASPC 461,
291; Pineau et al. 2020, ASPC 522, 125). Terms:
https://cds.unistra.fr/vizier-org/licences_vizier.html — use with
acknowledgement of VizieR and of each catalogue's paper, as done here.

## Catalogues

| Source | Rows used | What it gives |
|---|---|---|
| **Huchra, J. P. et al. 2012**, *The 2MASS Redshift Survey — Description and Data Release*, ApJS 199, 26 — VizieR J/ApJS/199/26 (`table3`) | 43,517 rows (of 44,599: 1,066 have no redshift and 16 are too slow to place with no measured distance) | position, heliocentric redshift cz, K_s magnitude (extinction-corrected total), K-band isophotal / total size, axis ratio, ZCAT morphological type |
| **2MASS Extended Source Catalog** (Skrutskie, M. F. et al. 2006, AJ 131, 1163; Jarrett, T. H. et al. 2000, AJ 119, 2498) — VizieR VII/233 (`xsc`), matched within 3″ | position angle (and axis ratio) of the 2MRS galaxies | |
| **Karachentsev, I. D., Makarov, D. I. & Kaisina, E. I. 2013**, *Updated Nearby Galaxy Catalog*, AJ 145, 101 — VizieR J/AJ/145/101 (`catalog`) | 859 rows (695 of them from UNGC alone; the Milky Way and the satellites the galaxy model draws are skipped) | distance and its method (TRGB, Cepheids, SBF, Tully-Fisher, …), Holmberg diameter, axis ratio, T-type, K magnitude / luminosity, velocity |
| **McConnachie, A. W. 2012**, *The Observed Properties of Dwarf Galaxies in and around the Local Group*, AJ 144, 4 — VizieR J/AJ/144/4 (`catalog`) | 79 rows (the Milky Way and the ten satellites the galaxy model draws are skipped) | distance with errors, half-light radius, ellipticity, position angle, absolute magnitude, velocity |
| **Tully, R. B. et al. 2023**, *Cosmicflows-4*, ApJ 944, 94 — VizieR J/ApJ/944/94 (`table2`, `groups`), matched within 6″ | 11,488 matches | measured distances of galaxies and group averages (TRGB / Cepheid zero point); group membership and mean group velocities |
| **OpenNGC** by Mattia Verga, release v20231203 (`NGC.csv`, `addendum.csv`), https://github.com/mattiaverga/OpenNGC — CC BY-SA 4.0 | the NGC / IC galaxies, matched by 2MASX identifier | NGC / IC / Messier names and cross-identifications (PGC, UGC), optical major / minor axis and position angle, Hubble type when 2MRS has none |
| `data/deep_sky.csv` (this repository; see `data/DEEP_SKY_LICENSE.md`) | 53 galaxies | position and distance of the galaxies the deep-sky layer already has (M31, M33, M81, M87 …) |

**2MASS acknowledgement.** This publication makes use of data products from
the Two Micron All Sky Survey, which is a joint project of the University of
Massachusetts and the Infrared Processing and Analysis Center/California
Institute of Technology, funded by the National Aeronautics and Space
Administration and the National Science Foundation.

## Derived values (what the game computes, and its tags)

* **Distance from redshift** — *inferred*: cz (2MRS) → CMB frame (Planck
  Collaboration 2020, A&A 641, A1: 369.82 km/s toward l 264.021°, b 48.253°),
  blended below ~4,000 km/s into the Local Group frame (Karachentsev & Makarov
  1996, AJ 111, 794: 316 km/s toward l 93°, b −4°), then
  D = (v / H0)(1 − 0.225 v/c), H0 = 70 km/s/Mpc, Ω_m = 0.3. Members of a
  Cosmicflows-4 group of three or more take their group's mean velocity.
* **Luminosity** — *inferred*: K magnitude + distance, M_K,⊙ = 3.28.
* **Size** — *inferred*: angular size × distance.
* **Tilt** — *model*: an oblate disc (intrinsic axis ratio 0.2 for spirals,
  0.3 for S0s) or spheroid matching the axis ratio and position angle; which
  way the disc leans toward us is not known, one of the two solutions is drawn.

Encoding: 32-byte header, then a gzip stream of float32 columns (RA, Dec,
distance, cz, second distance, diameter), uint8 columns (luminosity, normal,
axis ratio, T-type, class, methods, error, source bits, flags, K magnitude) and
the names (one line per galaxy: id | name | link | aliases). Layout:
`tools/build_galaxies.py` docstring.

## Morphology (`data/galaxies/morphology.bin`)

`data/galaxies/morphology.bin` (180 kB) gives each galaxy in `galaxies.bin` the
shape the map draws: bulge, bar, spiral arms (strength, count, pitch, which way
they turn on the sky), flocculence, rings, disturbance and dust. It is
generated by `tools/build_galaxy_morphology.py` from the sources below
(VizieR `asu-tsv` and the CDS XMatch service, as above). Downloads: 2026-10-03.
How the sources combine and how the game draws them: `docs/GALAXY.md`,
"Morphology". Same licence as `galaxies.bin` (CC BY-SA 4.0); keep the
citations below.

| Source | Rows used | What it gives |
|---|---|---|
| **Baillard, A. et al. 2011**, *The EFIGI catalogue of 4458 nearby galaxies with detailed morphology*, A&A 532, A74; **de Lapparent, V., Baillard, A. & Bertin, E. 2011**, A&A 532, A75 — VizieR J/A+A/532/A74 (`efigi`), matched within 10″ | 2,695 galaxies on the map; all 4,458 for the per-type medians | astronomers' grades (0, 0.25, 0.5, 0.75, 1) of bulge-to-total, arm strength, arm curvature, arm rotation, bar length, inner / outer / pseudo-rings, perturbation, dust, flocculence; T-type |
| **Walmsley, M. et al. 2023**, *Galaxy Zoo DESI: Detailed morphology measurements for 8.7M galaxies in the DESI Legacy Imaging Surveys*, MNRAS 526, 4768 — VizieR J/MNRAS/526/4768 (`catalog`), matched within 4″; also Zenodo 10.5281/zenodo.8360385 (**CC BY 4.0**) | 22,598 matches | deep-learning predictions of Galaxy Zoo volunteers' votes on DESI Legacy Survey images: smooth / featured, edge-on, bar strong / weak, bulge size, spiral winding, arm count, merging |
| **Willett, K. W. et al. 2013**, *Galaxy Zoo 2: detailed morphological classifications for 304,122 galaxies from the Sloan Digital Sky Survey*, MNRAS 435, 2835, with the debiased fractions of **Hart, R. E. et al. 2016**, MNRAS 461, 3663 — VizieR J/MNRAS/461/3663 (`table1`, selected columns), matched within 4″ | 6,773 matches | volunteers' vote fractions: features, edge-on, bar, spiral, bulge prominence, odd features (ring, disturbed, merger, dust lane), winding, arm count |

**Galaxy Zoo.** The Galaxy Zoo classifications were made possible by the
participation of hundreds of thousands of volunteers
(https://www.zooniverse.org/projects/zookeeper/galaxy-zoo/), whose
contributions are acknowledged at https://authors.galaxyzoo.org/.

Derived values (tags):

* **Measured** — a survey's grade or vote fractions mapped onto EFIGI's
  scales (the mapping is in the tool's docstring). Per attribute the first that
  measured it wins: EFIGI, Galaxy Zoo DESI, Galaxy Zoo 2.
* **Model** — the median of the EFIGI galaxies of the same T-type (the bar
  from the catalogue's B / X flag) for galaxies no survey graded.
* **Class** — 6,371 galaxies the catalogues left unclassified take a class
  from Galaxy Zoo where at least 60 % of the (conditional) votes agree.

Encoding: 32-byte header ("XGMORPH" 1, count, sizes, and `galaxies.bin`'s gzip
size as a key), then a gzip stream of twelve uint8 columns. Layout:
`tools/build_galaxy_morphology.py` docstring.

## Deep redshift surveys (`data/galaxies/deep.bin`, `data/galaxies/deep_more.bin`)

`data/galaxies/deep.bin` (107,204 galaxies, 2.5 MB; every build) and
`data/galaxies/deep_more.bin` (750,423 more, 17.3 MB; the native builds only)
add 857,627 galaxies of three optical redshift surveys that `galaxies.bin`
does not already have, carrying the cosmic web from ~700 Mly, where 2MRS thins
out, to ~3 Gly (`scripts/xgal_deep.gd`, drawn by `scripts/galaxies.gd`). They
are generated by `tools/build_galaxies_deep.py`, which downloads the tables
below from VizieR (`asu-tsv`) and can be rerun to reproduce them. Downloads:
2026-10-03. How they are deduplicated and placed: `docs/GALAXY.md`, "Deep
redshift surveys".

The files are a compilation of published measurements (no OpenNGC content), so
Expanse distributes them under **Creative Commons Attribution 4.0 (CC BY 4.0)**
— https://creativecommons.org/licenses/by/4.0/ — as compiled. VizieR terms as
above (https://cds.unistra.fr/vizier-org/licences_vizier.html): use with the
VizieR acknowledgement and each catalogue's paper. Please keep the citations
and acknowledgements below, which the surveys ask for.

| Source | Rows used | What it gives |
|---|---|---|
| **Tempel, E., Tuvikene, T., Kipper, R. & Libeskind, N. I. 2017**, *Merging groups and clusters of galaxies from the SDSS data*, A&A 602, A100 — VizieR J/A+A/602/A100 (`table1`): the SDSS DR12 main galaxy sample (Alam, S. et al. 2015, ApJS 219, 12; Legacy area, r < 17.77) | 574,805 (of 584,449: 9,626 are already in `galaxies.bin`; 18 slower than 300 km/s) | position, heliocentric redshift, extinction-corrected Petrosian r, friends-of-friends group and its richness; morphology probabilities (E, S0, Sab, Scd) from **Huertas-Company, M. et al. 2011**, A&A 525, A157 |
| **Jones, D. H. et al. 2009**, *The 6dF Galaxy Survey: final redshift release (DR3) and southern large-scale structures*, MNRAS 399, 683; **Jones, D. H. et al. 2004**, *The 6dF Galaxy Survey: samples, observational techniques and the first data release*, MNRAS 355, 747 — VizieR VII/259 (`6dfgs`), the Final Release of 6dFGS | 92,748 (of 109,832 with 6dFGS's own quality 3–4 redshift: 14,843 in `galaxies.bin`, 904 in SDSS, 1,337 slower than 300 km/s) | position, heliocentric cz, b_J magnitude, V-band extinction, designation |
| **Colless, M. et al. 2001**, *The 2dF Galaxy Redshift Survey: spectra and redshifts*, MNRAS 328, 1039; **Colless, M. et al. 2003**, *The 2dF Galaxy Redshift Survey: Final Data Release*, arXiv:astro-ph/0306581 — VizieR VII/250 (`2dfgrs`) | 190,074 (of 233,251 with quality ≥ 3: 1,332 in `galaxies.bin`, 29,621 in SDSS or 6dFGS, the rest stars or z > 0.3) | position, heliocentric redshift, b_J magnitude and Galactic extinction, designation |

**SDSS acknowledgement** (SDSS-III; DR12 is an SDSS-III release; text from
https://www.sdss3.org/collaboration/boiler-plate.php, as the SDSS asks for
data of its earlier phases):

> Funding for SDSS-III has been provided by the Alfred P. Sloan Foundation,
> the Participating Institutions, the National Science Foundation, and the
> U.S. Department of Energy Office of Science. The SDSS-III web site is
> http://www.sdss3.org/.
>
> SDSS-III is managed by the Astrophysical Research Consortium for the
> Participating Institutions of the SDSS-III Collaboration including the
> University of Arizona, the Brazilian Participation Group, Brookhaven National
> Laboratory, Carnegie Mellon University, University of Florida, the French
> Participation Group, the German Participation Group, Harvard University, the
> Instituto de Astrofisica de Canarias, the Michigan State/Notre Dame/JINA
> Participation Group, Johns Hopkins University, Lawrence Berkeley National
> Laboratory, Max Planck Institute for Astrophysics, Max Planck Institute for
> Extraterrestrial Physics, New Mexico State University, New York University,
> Ohio State University, Pennsylvania State University, University of
> Portsmouth, Princeton University, the Spanish Participation Group, University
> of Tokyo, University of Utah, Vanderbilt University, University of Virginia,
> University of Washington, and Yale University.

**6dFGS.** The survey asks (http://www-wfau.roe.ac.uk/6dFGS/, "How to
acknowledge the 6dF Galaxy Survey") that any use of the data "explicitly state
that they come from the Final Release of 6dFGS and cite both the 6dGS DR3 paper
(Jones et al 2009) as well as the original 6dFGS survey paper (Jones et al
2004, MNRAS 355, 747)": these galaxies come from the Final Release of 6dFGS
(Jones et al. 2009; Jones et al. 2004).

**2dFGRS.** Data from the 2dF Galaxy Redshift Survey (the 2dFGRS Team; Colless
et al. 2001, 2003), final data release as archived at VizieR (VII/250, from
http://www.mso.anu.edu.au/2dFGRS/). The survey's own pages were unreachable
when this was written (2026-10-03); credit and cite as above.

Derived values (what the game computes, and its tags):

* **Distance from redshift** — *inferred*, exactly as for 2MRS above (CMB /
  Local Group frame, H0 = 70 km/s/Mpc, D = (v / H0)(1 − 0.225 v/c)); SDSS
  members of a Tempel+ 2017 group of three or more take the group's mean
  redshift. 6dFGS / 2dFGRS galaxies take their own (no published groups).
* **Luminosity** — *inferred*: the survey's magnitude (SDSS r, b_J) + the
  luminosity distance, no k-correction; M_r,⊙ = 4.65, M_bJ,⊙ = 5.33;
  6dFGS b_J corrected by A_bJ = 1.30 A_V.
* **Type** (SDSS only) — *inferred*: Huertas-Company et al. 2011's automated
  classification, shown where one class has p ≥ 0.6 (E, S0, or Sab + Scd).
* **Group** (SDSS only) — *inferred*: Tempel et al. 2017's group finder.

Encoding: 32-byte header ("EXGDEEP" 1, count, sizes, `galaxies.bin`'s gzip
size as a key, the tier, the full count), then a gzip stream: float32 (x, y, z,
packed) per galaxy, int64 designations, int32 cz, five uint8 columns. Layout:
`tools/build_galaxies_deep.py` docstring.

## DESI DR1 (`data/galaxies/deep_desi.bin`, desktop builds only)

`data/galaxies/deep_desi.bin` (3,761,685 galaxies, ~85 MB; **not committed**:
built by `tools/build_galaxies_desi.py`, in CI by
`.github/actions/desi-galaxies`, and bundled by the desktop presets only) adds
the galaxies of the **Bright Galaxy Survey of DESI Data Release 1** that the
files above do not already have, out to z = 0.3 (`scripts/xgal_deep.gd`, drawn
by `scripts/galaxies.gd`). Source: the DR1 large-scale-structure clustering
catalogues `BGS_ANY_NGC_clustering.dat.fits` and `BGS_ANY_SGC_clustering.dat.fits`
(LSS v1.5, https://data.desi.lbl.gov/public/dr1/survey/catalogs/dr1/LSS/iron/LSScats/v1.5/),
downloaded 2026-10-17.

**Licence.** DESI data are licensed under the Creative Commons Attribution 4.0
International License (CC BY 4.0; https://data.desi.lbl.gov/doc/acknowledgments/).
Cite: DESI Collaboration et al. (2026), "Data Release 1 of the Dark Energy
Spectroscopic Instrument"; the Bright Galaxy Survey: Hahn, C. et al. 2023, AJ
165, 253. Expanse distributes the derived file under CC BY 4.0 too.

**Changes made** (as the licence asks): of the 5,522,353 clustering-catalogue
rows, only those with z ≤ 0.3 are kept (3,999,617); 6,734 that are already
`galaxies.bin` galaxies and 231,193 already in the SDSS / 6dFGS / 2dFGRS files
(within 6″ and 500 km/s) are dropped, and 5 that would share a truncated
designation with a nearer galaxy; each keeps only its position, its redshift
(converted to a distance, *inferred*, exactly as for the deep surveys above),
its Legacy Surveys r flux (as a magnitude and an *inferred* luminosity) and an
IAU-style designation made from its coordinates ("DESI JHHMMSS.ss+DDMMSS.s").

**DESI acknowledgement** (the text DESI asks every derived work to include):

> This research used data obtained with the Dark Energy Spectroscopic
> Instrument (DESI). DESI construction and operations is managed by the
> Lawrence Berkeley National Laboratory. This material is based upon work
> supported by the U.S. Department of Energy, Office of Science, Office of
> High-Energy Physics, under Contract No. DE–AC02–05CH11231, and by the
> National Energy Research Scientific Computing Center, a DOE Office of Science
> User Facility under the same contract. Additional support for DESI was
> provided by the U.S. National Science Foundation (NSF), Division of
> Astronomical Sciences under Contract No. AST-0950945 to the NSF's National
> Optical-Infrared Astronomy Research Laboratory; the Science and Technology
> Facilities Council of the United Kingdom; the Gordon and Betty Moore
> Foundation; the Heising-Simons Foundation; the French Alternative Energies and
> Atomic Energy Commission (CEA); the National Council of Humanities, Science
> and Technology of Mexico (CONAHCYT); the Ministry of Science and Innovation of
> Spain (MICINN), and by the DESI Member Institutions:
> www.desi.lbl.gov/collaborating-institutions. The DESI collaboration is
> honored to be permitted to conduct scientific research on I'oligam Du'ag
> (Kitt Peak), a mountain with particular significance to the Tohono O'odham
> Nation. Any opinions, findings, and conclusions or recommendations expressed
> in this material are those of the author(s) and do not necessarily reflect
> the views of the U.S. National Science Foundation, the U.S. Department of
> Energy, or any of the listed funding agencies.

## The cosmic web (`data/galaxies/filaments.bin`, `data/galaxies/structures.csv`, `data/galaxies/basins.bin`, `data/galaxies/basins_groups.bin`, `data/galaxies/voids.bin`, `data/galaxies/local_voids.bin`)

Built by `tools/build_cosmic_web.py` (downloads cached in `tools/.xgal_cache/`,
2026-10-17); drawn by `scripts/cosmic_web.gd`. Both files are compilations of
published measurements, distributed under **CC BY 4.0** as compiled.

| Source | Rows used | What it gives |
|---|---|---|
| **Tempel, E., Stoica, R. S., Martínez, V. J., Liivamägi, L. J., Castellan, G. & Saar, E. 2014**, *Detecting filamentary pattern in the cosmic web: a catalogue of filaments for the SDSS*, MNRAS 438, 3465 — CDS J/MNRAS/438/3465 (`table1`, `table2`; `table3` only to check the frame) | all 15,421 filaments, 275,599 spine points | each filament's spine (comoving coordinates in Mpc/h, the SDSS survey frame), length, galaxy counts within 0.5 and 1 Mpc/h, their r-band luminosity, the per-point filament strength (weighted visit map) — traced through the SDSS DR8 main galaxy sample (SDSS-III acknowledgement above) |
| **Dupuy, A. & Courtois, H. M. 2023**, *Dynamic cosmography of the local Universe: Laniakea and five more watershed superclusters*, A&A 678, A176 — basins-of-attraction and -repulsion grids `CF4_new_128-z008_BoA.fits`, `CF4_new_128-z008_BoR.fits` and the grouped reconstruction's `CF4gp_new_128-z008_BoA.fits`, `CF4gp_new_128-z008_BoR.fits` from https://projets.ip2i.in2p3.fr/cosmicflows/ (`CF4_new_128-z008_watersheds-fits.zip`, downloaded 2026-10-17; the page asks users to cite the article); built on the CF4 velocity field of **Courtois, H. M. et al. 2023**, A&A 670, L15, from **Cosmicflows-4**, Tully, R. B. et al. 2023, ApJ 944, 94 | basins 1–9 (Laniakea, Apus, Hercules, Lepus, Perseus–Pisces, Shapley, SDSS-1a, SDSS-2a, SDSS-2b) → `data/galaxies/basins.bin`; the grouped grids' basins of attraction 1–11 and of repulsion 1–5 → `data/galaxies/basins_groups.bin`; basins of repulsion 1–3 (the Sculptor Void, near the Boötes Void, the Dipole + Cold Spot Repeller) → `basins.bin`; Table A.1's attractor and repeller positions (both reconstructions' columns) for Apus, Lepus, the SDSS basins and the repellers → `structures.csv` | each basin's surface (smoothed, marching cubes), placed by the map's Hubble-law distance; its volume |
| **Douglass, K. A., Veyrat, D. & BenZvi, S. 2023**, *Updated void catalogs of the SDSS DR7 main sample*, ApJS 265, 7 — CDS J/ApJS/265/7 (`table1`, `table2`, `table3`; both runs, Planck 2018 and WMAP5) | VoidFinder's 1,163 voids (maximal spheres, effective radii, edge flags, and all 39,735 hole spheres, whose union each void is: centres and radii); V²/VIDE's 531 and V²/REVOLVER's 518 voids (weighted centres, z, effective radii, ellipsoid axes, surface and edge areas) → `data/galaxies/voids.bin` | each void's centre, size and shape as the void finders measured them on the SDSS DR7 volume-limited sample (NSA v1.0.1) |
| **Malandrino, R., Lavaux, G., Wandelt, B. D., McAlpine, S. & Jasche, J. 2026**, *A Bayesian catalog of 100 high-significance voids in the Local Universe*, A&A 705, A160 — github.com/RosaMalandrino/LocalVoids (commit bbbc345, read 2026-10-17; `voids_catalog.csv`, `VoronoiClouds/`; no licence stated) | all 100 voids: posterior centres and radii with their spreads, redshifts of the near / far edge, each void's 32³ Voronoi-overlap grid → `data/galaxies/local_voids.bin` | each void's centre, size and shape in the Manticore-Local reconstruction of the 2M++ galaxies |
| The papers named per row in `structures.csv` (`source`, `dist_src`, `size_src`): de Vaucouleurs 1953; Tully 1982; Tully, Courtois, Hoffman & Pomarède 2014; Lynden-Bell et al. 1988; Kraan-Korteweg et al. 1996; Woudt et al. 2008; Lucey, Currie & Dickens 1986; Struble & Rood 1999; Blakeslee et al. 2009; Ferguson 1989; Haynes & Giovanelli 1986; Giovanelli, Haynes & Chincarini 1986; Zwicky 1933; Geller & Huchra 1989; Chincarini, Rood & Thompson 1981; Kirshner et al. 1981, 1987; Tully & Fisher 1987; Tully et al. 2008; Shapley 1930; Raychaudhury 1989; Proust et al. 2006; Lucey et al. 1983; Fleenor et al. 2005; Postman, Geller & Huchra 1988; Gott et al. 2005; Einasto et al. 2011; Mei et al. 2007; Hoffman, Pomarède, Tully & Courtois 2017 (Nature Astronomy 1, 0036); Courtois et al. 2017 (ApJ 847, L6); Dupuy & Courtois 2023 | 32 named structures | centre (RA / Dec or l / b), redshift or measured distance, approximate size |

Derived values (what the game computes, and its tags):

* **Filament placement** — each spine point is turned back into (RA, Dec, z)
  (the SDSS survey frame: node 95°, inclination 32.5°, checked against the
  catalogue's own galaxies; z from the comoving distance on the paper's
  cosmology, Ω_m = 0.27) and placed by the map's own redshift rule
  (*inferred*, as the deep surveys above), so a filament lies on the galaxies
  that trace it. Lengths and counts are the catalogue's (*measured*); lengths in
  light-years and luminosities take h = 0.7.
* **Structure distances** — *measured* where the row names a measured distance
  (Virgo, Fornax, the Local Void's centre), else from the redshift by the map's
  rule (*inferred*); sizes are the papers' approximate extents (*inferred*).

* **The basins' outlines** — *model*: smoothed level surfaces of the
  watershed's basins of attraction 1–9 and of repulsion 1–3 (Gaussian 0.8
  voxel, level 0.5), each vertex at the map's Hubble-law distance for
  cz = 100 r km/s; the Dipole + Cold Spot basin and the SDSS basins, which run
  past the box, are left open where the box cuts them; the same for the
  grouped reconstruction's 11 + 5 (`basins_groups.bin`).

* **Void placement** — each centre's comoving distance back to z on Planck 2018,
  then heliocentric cz and the map's rule (*inferred*); its shape through the
  placement's local stretch. Effective radii, maximal spheres and axes are the
  catalogue's (*measured* by its void finder); lengths in light-years take
  h = 0.7.

Encoding of `filaments.bin`: 32-byte header ("EXGFILA" 1, filaments, points,
payload size, gzip size), then a gzip stream: float32 (x, y, z, strength) per
point, then per filament int32 first point, int32 point count, float32 length
(ly), float32 luminosity (L☉), uint16 galaxies within 0.5 and 1 Mpc/h. Layout:
`tools/build_cosmic_web.py` docstring.