Europe map -- data sources and attribution
==========================================

Built by mapgen.py (with mapgen_continent.py) from configs/europe.json on 2026-10-09.
Every input is public and needs no account or key. Rebuilt from open data in Front+ 1.0.6
in place of the OpenFront map of the same name (CC BY-SA); nothing of that map is used
except its size, the shape it was fitted to (see Geometry) and its nations' names, flags
and spawn places.

Datasets used
-------------
Land        Natural Earth 1:10m Physical Vectors, PUBLIC DOMAIN (https://www.naturalearthdata.com,
            'Made with Natural Earth'; no permission needed). Downloaded from
            https://naciscdn.org/naturalearth/10m/physical/<layer>.zip
            ne_10m_land (version 5.1.1, 6836 polygon parts), ne_10m_minor_islands (version 4.1.0, 683 polygon parts):
            every land polygon in the map's box is land (no country is cut out).
Lakes       Natural Earth 1:10m (ne_10m_lakes, ne_10m_lakes_europe), public domain.
Rivers      Natural Earth 1:10m ne_10m_rivers_lake_centerlines (version 5.0.0), public domain.
Elevation   ETOPO 2022 Global Relief Model v1, ice surface elevation, NOAA National Centers for
            Environmental Information. PUBLIC DOMAIN (a work of the U.S. Government; NOAA: "freely
            available to use for all private, academic, or commercial purposes"). From
            https://www.ncei.noaa.gov/products/etopo-global-relief-model, files:
            ETOPO_2022_v1_15s_N30W030_surface.tif,
            ETOPO_2022_v1_15s_N30W015_surface.tif,
            ETOPO_2022_v1_15s_N30E000_surface.tif,
            ETOPO_2022_v1_15s_N30E015_surface.tif,
            ETOPO_2022_v1_15s_N30E030_surface.tif,
            ETOPO_2022_v1_15s_N30E045_surface.tif,
            ETOPO_2022_v1_15s_N45W030_surface.tif,
            ETOPO_2022_v1_15s_N45W015_surface.tif,
            ETOPO_2022_v1_15s_N45E000_surface.tif,
            ETOPO_2022_v1_15s_N45E015_surface.tif,
            ETOPO_2022_v1_15s_N45E030_surface.tif,
            ETOPO_2022_v1_15s_N45E045_surface.tif,
            ETOPO_2022_v1_15s_N60W030_surface.tif,
            ETOPO_2022_v1_15s_N60W015_surface.tif,
            ETOPO_2022_v1_15s_N60E000_surface.tif,
            ETOPO_2022_v1_15s_N60E015_surface.tif,
            ETOPO_2022_v1_15s_N60E030_surface.tif,
            ETOPO_2022_v1_15s_N60E045_surface.tif,
            ETOPO_2022_v1_15s_N75W030_surface.tif,
            ETOPO_2022_v1_15s_N75W015_surface.tif,
            ETOPO_2022_v1_15s_N75E000_surface.tif,
            ETOPO_2022_v1_15s_N75E015_surface.tif,
            ETOPO_2022_v1_15s_N75E030_surface.tif,
            ETOPO_2022_v1_15s_N75E045_surface.tif
            (15 arc-second cells). Cite as:
            NOAA National Centers for Environmental Information. 2022: ETOPO 2022 15
            Arc-Second Global Relief Model. NOAA National Centers for Environmental
            Information. DOI: 10.25921/fd45-gt74.
            ETOPO 2022's land elevation is built from, among others, Copernicus DEM 30 m,
            credited by NOAA's User Guide as: The European Space Agency. Copernicus DEM - Global
            and European Digital Elevation Model (COP-DEM); and FABDEM (Hawker et al. 2022,
            Environmental Research Letters 17(2), 024016, doi:10.1088/1748-9326/ac4d4f).

Geometry
--------
Projection      +proj=eqc +lat_ts=1.4062 +lon_0=12.5000 +ellps=WGS84 +units=m +no_defs (pyproj 3.8.0)
                equirectangular (plate carree) with true scale along 1.4 N: the projection the old map
                fits best (fit_old.py; IoU 0.950 at 16x with its river channels as land, 0.896 as it is;
                Miller 0.697, Mercator 0.669, Lambert conformal conic 0.668). A degree of longitude and a
                degree of latitude are nearly the same number of tiles, as on the old map. Not conformal:
                a tile is 2,740 m tall everywhere and, on the ground, 2,373 m wide at 30.1 N, 1,765 m at
                50 N and 881 m at 71.3 N; the game treats tiles as square, so no aspect correction is used.
Fitted          by fit_old.py to the old map's land (its map16x.bin): the eqc projection
                and box under which Natural Earth's land, rasterised on the old grid, best matches
                the old land: intersection over union 0.8963 at 16x (0.9495 with the old map's one-tile river channels counted as land).
Grid            2904 x 1672 tiles at 2739.7 m/tile (7956.0 x 4580.7 km), the old map's size
Origin          tile (x,y) covers E = -4146310.0 + 2739.7*x, N = 7912506.0 - 2739.7*y
Latitude        row 0 = 71.3 N, last row = 30.1 N (crates/of_app/src/view.rs
                latitude_range: "europe" => (71.3, 30.1)), set in the config:
                the centre column (a row is a parallel in this projection).
                Centre column (71.3, 30.1): off by 0.02 deg on average over the land (0.03 at worst);
                least squares (71.3, 30.1): 0.01 deg (0.03 at worst).

Coastline       Natural Earth's outline refined by ETOPO 2022: a tile is land when at least half of
                its ETOPO cells are above 0 m (5.89 to ~5.91 cells across a
                tile), within 3 km of Natural Earth's coast inside the land and within
                40 km of it out at sea (the small islands Natural Earth leaves out);
                deeper inland Natural Earth decides. ETOPO made 15,203 tiles land that Natural Earth
                has as sea and 6,636 the other way.
Elevation curve magnitude = round(curve(u)), clamped 0..31, where e is the tile's mean ETOPO
                elevation (area average of its cells) and u = e - 0.3*(e - gaussian(e, sigma = 2 tiles)),
                the blur taken over land only so the sea does not drag the coast down.
                The curve is the auto_bands fit on the field u with the old map's own band shares: 57%
                of the land is Plains, 13% Mountain (the old Europe measured 57-30-13, slope 1.16, rock
                29%), the top segment running to the highest u so peaks are not clamped. The mask (-0.3
                over a 2-tile sigma, a light softening) is the --tune row whose slope is nearest 0.6 with
                rock under 12%: 0.59 and 10.2%. Measured alternatives: no mask 0.61 / 10.9%; -0.3 over 4
                tiles 0.57 / 9.5%; +1 over 2 tiles 0.70 / 13.7%; +2 over 2 tiles 0.79 / 16.9%.
                curve: auto_bands {'plains': 0.57, 'mountain': 0.13} -> piecewise-linear [[0.0, 0.0], [237.1, 9.5], [868.8, 19.5], [3325.1, 31.0]].
                Result: mean slope 0.596 magnitude steps/tile, 10.29% rock, bands
                57.0% Plains / 30.0% Highland / 13.0% Mountain, mean magnitude 9.61
                (Switzerland 0.62 / 8.8% / 51-34-15 / 11.10, Britannia 0.67 / 12.4% / 39-53-9 / 10.12,
                measured the same way by validate_map.py).
                map4x / map16x: slope 0.93 / 1.432, rock 19.11% / 33.25%.
Water magnitude OpenFront's convention: min(ceil(d/2), 31), d = Manhattan distance from the
                shoreline water.
Lake policy     Natural Earth lakes are lakes; a lake that touches the map's edge, the sea or a
                river that reaches the sea is ocean. A lake under 40 tiles at full res (300.2 km2),
                10 at 4x or 3 at 16x is filled back to land at the ground height.
Island policy   land bodies under 2 tiles at full resolution are dropped; every island that survives the downsample is kept at 4x and 16x.
Downsampling    map4x / map16x: plurality vote of each 2x2 block (a 2-2 tie goes to the side
                with the larger sub-tile land fraction); sea cut off by the vote is reconnected
                along its real channel; then the small-body cleanup above. 16x is built from 4x.
                Carved channel tiles: 4x 47, 16x 63.
River policy    Natural Earth centre lines (all) burnt as water:
                every tile whose centre is within 0.71 tile of the line (3.9 km wide at full
                resolution),
                and burnt again from the same lines into map4x and map16x (half width 0.71 tile)
                after the plurality vote, so each river is one continuous 4-connected channel at
                every resolution. A river that reaches the sea is ocean, so boats can use it.
                A river mouth short of other water by <= 10 tiles is extended to it
                (to water of at least 40 tiles, not to a speck); a river's lower end only, by ETOPO's elevation, never its source.
                Natural Earth's lake centre lines are burnt too (a river's course through its
                lakes and reservoirs), so a reservoir narrower than a tile does not cut the river.
Landmasses      map4x and map16x keep the landmasses of the finer detail. Two that are
                apart stay apart (where the vote closed the water between them, a tile over
                both becomes water: 10 tiles at 4x, 2 at 16x), and one piece stays one
                (where a river burnt one tile wide would split it, two sources a coarse tile
                apart, the highest one-tile water between the pieces becomes land:
                8 tiles at 4x, 18 at 16x).
                The old map had river water: 42,828 tiles of one- and two-tile channels at full detail,
                open to the sea, at all three resolutions. The same rivers are burnt here from Natural
                Earth's centre lines with scalerank <= 12, the cut whose lines best match the old
                channels (fit_old.py: 44,669 tiles, 77% of them within 3 tiles of an old
                channel, 65% of the old channels within 3 tiles of one), one tile wide.
Estuaries       a river system cut off from the sea (Natural Earth's line stops where its estuary
                begins, and the estuary, narrower than a tile and at ETOPO's water surface above
                0 m, is land on the grid) is joined to the sea along the cheapest path over low
                ground: land tiles no higher than 30 m, at most 60 of them, burnt one tile
                wide and carried to map4x and map16x: 13 river systems, 160 tiles.
Straits         kept open: Bosporus, Dardanelles, Oresund, Little Belt, Strait of Messina: the strait's centre line (traced on
                ETOPO's cells below sea level) burnt as water like a river, at every detail.
                The Bosporus (under a kilometre at its narrowest), the Dardanelles (1.2 km), the Little Belt
                (0.7 km at Middelfart), the Oresund (4 km at Helsingor) and the Strait of Messina (3 km)
                close on this grid at one detail or more by themselves; each carries a line traced on ETOPO,
                so all five are open at every detail, as on the old map. Gibraltar, the Great Belt, the Kerch
                Strait, Otranto and the Strait of Dover are open by themselves at every detail, as on the
                old map. compare_old_europe.txt checks each strait inside its own box.

Climate (climate.bin)
---------------------
Source      Beck, H.E., N.E. Zimmermann, T.R. McVicar, N. Vergopolan, A. Berg, E.F. Wood:
            Present and future Koppen-Geiger climate classification maps at 1-km
            resolution, Scientific Data 5, 180214 (2018), doi:10.1038/sdata.2018.214.
            Data: figshare, doi:10.6084/m9.figshare.6396959 (Beck_KG_V1.zip, no login),
            Beck_KG_V1_present_0p0083.tif (present day, 1980-2016, ~1 km).
            Licence CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/):
            attribution required; the classes were turned into moisture values
            and reprojected (changes made).
Grid        the map16x grid, 726 x 418: one byte per 16x tile, 0 = driest, 255 = wettest,
            on the terrain shader's own moisture scale (x 255).
Method      each Koppen class -> a moisture (table below); reprojected with the map's
            projection, each 16x tile the area average of the 1 km cells in it; the sea
            and the neighbours (water on this map) take the nearest own land's value;
            Gaussian smoothing, sigma 8 km (1.0 tiles of 10.96 km).
Classes     BWh, BWk 0.06; BSh, BSk 0.28; Csa 0.34; Dsa 0.40; Csb, Csc, Dsb 0.46;
            Dsc, Dsd 0.48; Aw, ET, EF 0.50; Cwa, Cwb, Cwc, Dwa, Dfa 0.52;
            Cfb, Cfc, Dwb, Dwc, Dwd, Dfb 0.53; Dfc, Dfd 0.58; Cfa 0.60; Am 0.66; Af 0.76.
            The shader's temperate ladder: desert under 0.22, steppe to 0.33, grass
            to 0.56, forest above; in hot country savanna from 0.24, grass from 0.45,
            jungle above 0.56. Tundra and snow come from the temperature.
Land        the largest classes by 16x land tile: Dfb 30%, Dfc 21%, BWh 10%, Cfb 9%, BSk 8%,
            Csa 7%, ET 3%, Dfa 3%, BWk 2%, Dsb 2%, Cfa 2%, BSh 1%, Csb 1%.
            As the temperate ladder reads it: desert 12.0%, steppe 8.6%,
            grass 58.6%, forest 20.8% (before the shader's noise, heat
            and altitude).

Colour (colour.jpg)
-------------------
Source      the ESA WorldCover Sentinel-2 median L2A (RGBNIR) composite of 2021, v200 (the
            ESA WorldCover project; made by the ESA WorldCover consortium from Copernicus
            Sentinel-2 data), its true-colour bands B04, B03 and B02 (the NIR band not
            used): one cloud-optimised GeoTIFF a 1 x 1 degree cell in the open-data bucket
            https://esa-worldcover-s2.s3.eu-central-1.amazonaws.com/rgbnir/2021/<band>/ESA_WorldCover_10m_2021_v200_<tile>_S2RGBNIR.tif,
            read at its overview level 4 (750 pixels a degree), only that level, by range
            requests (Front+ 1.0.9 step s02, 16 October 2026; every piece in
            mapdata/DOWNLOADS.txt). 1901 cells used; of the cells under the land and its
            one-tile ring 0 the bucket does not have (open sea) and 0 are missing.
Licence     CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/); the terms:
            https://esa-worldcover.org/en/data-access ("provided free of charge, without
            restriction of use").
Attribution © ESA WorldCover project / Contains modified Copernicus Sentinel data (2021) processed by ESA WorldCover consortium
Grid        the full map grid, 2904 x 1672: RGB, 8 bits a channel, sRGB, one texel a tile
            (2.740 km in the map's projection); JPEG, quality 90.
Changed     the source pixels averaged in blocks of 6 x 6 (3.1 x 3.1 of them a texel,
            north-south x east-west, at the land's middle), reprojected with the map's
            projection onto its grid, each texel the area average of the pixels in it in
            linear light (reflectance); water left out by the map's own land mask, and
            within 2 tiles of the map's own water also the imagery's own water (dark and
            blue pixels); clouds left out under the game's snow line (mean reflectance over
            1.50 and spread under 0.05 of the mean; 89 texels touched); the 12,863 land
            texels with no data or mostly left-out pixels filled from the land round them,
            every texel that is not land from the nearest land texel; the tone: 1.6 x
            reflectance, to the power 0.9, highlights rolled off above 0.6, the colours 1.45
            x as far from grey, exposure 1. Built 2026-10-16 (mapgen_imagery.py).
Land        mean colour 118, 114, 90 (sRGB), spread 45 / 30 / 27; 35 of 2,356,424 land
            texels had no source pixel with data (0.00%).
Game        the terrain shader takes the land's base colour from this instead of its
            biome palette, under its own light, relief shading, territory tint,
            borders, haze, snow and water, while the Realistic look is on (the
            Settings switch is the default for every map; each map can change it
            on the Singleplayer page; off, it draws the palette). Land a match
            raises where this map has sea keeps the palette.

Nations
-------
The old map's 52 nations, with their names and flags exactly as its manifest had them and
in its order. Each spawn is the lon/lat of the old spawn tile on the fitted grid, snapped
to the nearest tile that is land at all three resolutions, on the landmass of the land
nearest that point, off the 16x coast where one is within 8 tiles more. Each nation's spawn
must then lie in its own country (Natural Earth's admin-0 map units; England, Wales,
Scotland and Northern Ireland their own units): where the old spot is across a border on
the real coast, it moves to the nearest tile of its country that is land at all three
resolutions (the moves are named below). Sapmi, a cultural region, and Kazakhstan, of which
the map shows only a sliver at its east edge, keep their old spots.

  Ireland        ie         ( 634,  781)  the old map's spawn (634, 781) on the fitted grid; snapped 0 tiles
  England        gb-eng     ( 962,  780)  the old map's spawn (962, 780) on the fitted grid; snapped 0 tiles
  Spain          es         ( 874, 1286)  the old map's spawn (874, 1286) on the fitted grid; snapped 0 tiles
  France         fr         (1087,  983)  the old map's spawn (1087, 983) on the fitted grid; snapped 0 tiles
  Italy          it         (1541, 1180)  the old map's spawn (1541, 1180) on the fitted grid; snapped 0 tiles
  Switzerland    ch         (1339,  997)  the old map's spawn (1339, 997) on the fitted grid; snapped 0 tiles
  Norway         no         (1360,  428)  the old map's spawn (1360, 428) on the fitted grid; snapped 0 tiles
  Sweden         se         (1609,  477)  the old map's spawn (1609, 477) on the fitted grid; snapped 0 tiles
  Finland        fi         (2032,  346)  the old map's spawn (2032, 346) on the fitted grid; snapped 0 tiles
  Belgium        be         (1182,  836)  the old map's spawn (1182, 836) on the fitted grid; snapped 0 tiles
  Netherlands    nl         (1268,  764)  the old map's spawn (1268, 764) on the fitted grid; snapped 0 tiles
  Germany        de         (1445,  821)  the old map's spawn (1445, 821) on the fitted grid; snapped 0 tiles
  Austria        at         (1508,  960)  the old map's spawn (1507, 959) on the fitted grid; that spot is not in Austria on Natural Earth's map, so it moved 1 tiles to the nearest tile of it that is land at all three resolutions; snapped 1.4 tiles
  Poland         pl         (1751,  767)  the old map's spawn (1751, 772) on the fitted grid; snapped 5 tiles
  Czechia        cz         (1618,  874)  the old map's spawn (1618, 874) on the fitted grid; snapped 0 tiles
  Ukraine        ua         (2231,  885)  the old map's spawn (2231, 885) on the fitted grid; snapped 0 tiles
  Belarus        by         (2206,  676)  the old map's spawn (2206, 676) on the fitted grid; snapped 0 tiles
  Romania        ro         (2046,  990)  the old map's spawn (2046, 990) on the fitted grid; snapped 0 tiles
  Türkiye        tr         (2334, 1313)  the old map's spawn (2334, 1313) on the fitted grid; snapped 0 tiles
  Morocco        ma         ( 769, 1535)  the old map's spawn (769, 1535) on the fitted grid; snapped 0 tiles
  Russia         ru         (2591,  610)  the old map's spawn (2591, 610) on the fitted grid; snapped 0 tiles
  Syria          sy         (2538, 1418)  the old map's spawn (2538, 1418) on the fitted grid; snapped 0 tiles
  Iraq           iq         (2689, 1441)  the old map's spawn (2689, 1441) on the fitted grid; snapped 0 tiles
  Georgia        ge         (2746, 1143)  the old map's spawn (2748, 1138) on the fitted grid; that spot is not in Georgia on Natural Earth's map, so it moved 5 tiles to the nearest tile of it that is land at all three resolutions; snapped 5.4 tiles
  Tunisia        tn         (1359, 1473)  the old map's spawn (1359, 1473) on the fitted grid; snapped 0 tiles
  Algeria        dz         (1066, 1506)  the old map's spawn (1066, 1506) on the fitted grid; snapped 0 tiles
  Portugal       pt         ( 680, 1254)  the old map's spawn (680, 1254) on the fitted grid; snapped 0 tiles
  Greece         gr         (1891, 1299)  the old map's spawn (1891, 1299) on the fitted grid; snapped 0 tiles
  Serbia         rs         (1906, 1113)  the old map's spawn (1906, 1113) on the fitted grid; snapped 0 tiles
  Hungary        hu         (1751,  983)  the old map's spawn (1751, 983) on the fitted grid; snapped 0 tiles
  Slovakia       sk         (1826,  902)  the old map's spawn (1826, 902) on the fitted grid; snapped 0 tiles
  Croatia        hr         (1625, 1039)  the old map's spawn (1624, 1038) on the fitted grid; that spot is not in Croatia on Natural Earth's map, so it moved 1 tiles to the nearest tile of it that is land at all three resolutions; snapped 1.4 tiles
  Bosnia and Herzegovina ba         (1738, 1107)  the old map's spawn (1738, 1107) on the fitted grid; snapped 0 tiles
  Albania        al         (1817, 1213)  the old map's spawn (1817, 1213) on the fitted grid; snapped 0 tiles
  Bulgaria       bg         (2092, 1158)  the old map's spawn (2092, 1158) on the fitted grid; snapped 0 tiles
  Lithuania      lt         (1959,  704)  the old map's spawn (1958, 704) on the fitted grid; that spot is not in Lithuania on Natural Earth's map, so it moved 1 tiles to the nearest tile of it that is land at all three resolutions; snapped 1 tiles
  Latvia         lv         (2030,  614)  the old map's spawn (2030, 617) on the fitted grid; that spot is not in Latvia on Natural Earth's map, so it moved 3 tiles to the nearest tile of it that is land at all three resolutions; snapped 3 tiles
  Estonia        ee         (2052,  516)  the old map's spawn (2052, 516) on the fitted grid; snapped 0 tiles
  Wales          gb-wls     ( 863,  775)  the old map's spawn (863, 775) on the fitted grid; snapped 0 tiles
  Scotland       gb-sct     ( 841,  603)  the old map's spawn (841, 603) on the fitted grid; snapped 0 tiles
  Kazakhstan     kz         (2890,  857)  the old map's spawn (2890, 857) on the fitted grid, kept: the map shows only a sliver of Kazakhstan at its east edge, south of this spot; snapped 0 tiles
  Northern Ireland northern_ireland ( 719,  685)  the old map's spawn (719, 685) on the fitted grid; snapped 0 tiles
  Sápmi          Sami flag  (1900,  132)  the old map's spawn (1900, 132) on the fitted grid; snapped 0 tiles
  Denmark        dk         (1377,  625)  the old map's spawn (1377, 625) on the fitted grid; snapped 0 tiles
  Israel         il         (2406, 1638)  the old map's spawn (2406, 1638) on the fitted grid; snapped 0 tiles
  Egypt          eg         (2226, 1661)  the old map's spawn (2226, 1661) on the fitted grid; snapped 0 tiles
  Libya          ly         (1847, 1652)  the old map's spawn (1847, 1652) on the fitted grid; snapped 0 tiles
  Jordan         jo         (2535, 1608)  the old map's spawn (2535, 1609) on the fitted grid; that spot is not in Jordan on Natural Earth's map, so it moved 1 tiles to the nearest tile of it that is land at all three resolutions; snapped 1 tiles
  Lebanon        lb         (2468, 1530)  the old map's spawn (2473, 1528) on the fitted grid; that spot is not in Lebanon on Natural Earth's map, so it moved 5 tiles to the nearest tile of it that is land at all three resolutions; snapped 5.4 tiles
  Iceland        is         ( 268,  265)  the old map's spawn (266, 265) on the fitted grid; snapped 2 tiles
  Andorra        ad         (1064, 1167)  the old map's spawn (1045, 1188) on the fitted grid; that spot is not in Andorra on Natural Earth's map, so it moved 28 tiles to the nearest tile of it that is land at all three resolutions; snapped 28.3 tiles
  Monaco         mc         (1305, 1119)  the old map's spawn (1290, 1121) on the fitted grid; that spot is not in Monaco on Natural Earth's map, so it moved 15 tiles to the nearest tile of it that is land at all three resolutions; snapped 15.1 tiles