USA map -- data sources and attribution ======================================= Built by mapgen.py from configs/usa.json on 2026-09-28. Every input is public and needs no account or key. Datasets used ------------- Borders Natural Earth 1:10m Cultural Vectors, version 5.1.1. PUBLIC DOMAIN (https://www.naturalearthdata.com, 'Made with Natural Earth'; no permission needed, attribution appreciated). Downloaded from https://naciscdn.org/naturalearth/10m/cultural/.zip ne_10m_admin_0_countries: USA is the land (149 polygon parts; 195 parts outside clip_lonlat dropped); the neighbours (Bahamas, Canada, Mexico) are sea, and split the sea with it for islands. ne_10m_admin_1_states_provinces: the nations' regions. ne_10m_populated_places: the nations' spawn points. Lakes Natural Earth 1:10m Physical Vectors (ne_10m_lakes, ne_10m_lakes_north_america), public domain, https://naciscdn.org/naturalearth/10m/physical/.zip Elevation AWS Open Data Terrain Tiles (Mapzen/Tilezen 'terrarium' PNG tiles), zoom 8 (818 tiles) for the relief and zoom 12 (5336 tiles) along the coast for the coastline, https://s3.amazonaws.com/elevation-tiles-prod/terrarium/{z}/{x}/{y}.png (registry: https://registry.opendata.aws/terrain-tiles/). A compilation of public DEMs; the ones covering this area and their required credit: * SRTM and GMTED2010 terrain data courtesy of the U.S. Geological Survey (NASA/USGS, public domain); * Global ETOPO1 terrain data U.S. National Oceanic and Atmospheric Administration (public domain; the sea floor, used only to tell sea from land); * United States 3DEP (formerly NED) terrain data courtesy of the U.S. Geological Survey (public domain); * Canada terrain data contains information licensed under the Open Government Licence - Canada; * Mexico terrain data source: INEGI, Continental relief, 2016 (Canada and Mexico lie in the fetched tiles along the borders; they are water on this map, so their elevations are never used). Full attribution list: https://github.com/tilezen/joerd/blob/master/docs/attribution.md Geometry -------- Projection EPSG:5070 (pyproj 3.8.0); NAD83 / Conus Albers, equal-area (not conformal) as requested for the lower 48; metric. The game treats tiles as square: the scale along parallels differs from the scale along meridians by at most ~2.5 % (the map's north and south edges, beyond the 29.5 N / 45.5 N standard parallels) and by under 1 % across most of the land, so no aspect correction is used. Grid 2200 x 1388 tiles at 2110.1 m/tile (4642.2 x 2928.8 km) Origin tile (x,y) covers E = -2371086.4 + 2110.1*x, N = 3186587.4 - 2110.1*y (bounding box of the land plus 15 km of sea). Latitude row 0 = 50.3 N, last row = 25.4 N (crates/of_app/src/view.rs latitude_range: "usa" => (50.3, 25.4)), set in the config: a least-squares fit of latitude against row over every land tile. EPSG:5070 is conic, so a row is not a parallel: row 0 runs from 48.0 N at the corners to 51.7 N at the centre column, the last row from 22.8 N to 25.4 N. The centre-column pair (51.7, 25.4) is off by 0.78 deg on average over the land (3.2 deg at worst, Washington's north coast); the fit (50.3, 25.4) by 0.60 deg (2.2 deg at worst). Coastline the Natural Earth outline refined by the DEM: a tile is land when at least half of it is DEM land (terrarium elevation > 0 m; zoom 12 pixels of ~30 m, because at zoom 11 and below the tiles fill the sea near the coast from ETOPO1's 1.8 km cells and close narrow straits such as Salamis), restricted to the sea nearer to USA than to any neighbour and within 40 km of its coast (this adds the small islands Natural Earth 1:10m leaves out); more than 3 km inside the Natural Earth outline a tile is always land. Land borders are exactly Natural Earth's. Everything outside the border is water (the Switzerland rule). Elevation curve magnitude = round(curve(u)), clamped 0..31, where e is the tile's mean elevation (zoom 8 tiles, averaged into the tile) and u = e + 3*(e - gaussian(e, sigma = 4 tiles)), the blur taken over land only so the sea does not drag the coast down. The curve is the auto_bands fit (--tune) on the sharpened field u: half the land below 458 m is Plains, 17% above 1535 m is Mountain, and the top segment runs to the highest u so peaks are not clamped. The mask is stronger than Switzerland's (+3 over a 4-tile sigma, 8.4 km, instead of +2 over 2 tiles, 350 m): the lower 48 are mostly vast gentle plains, and at 2.1 km per tile the renderer's 9-tile smoothing would flatten the Appalachians, Ozarks and the basin-and-range to a slope of 0.27 (no mask) - 0.39 (Switzerland's +2 / 2 tiles). Measured alternatives: Switzerland's own recipe (120 m per step, +2) makes the lower 48 72% Plains with a slope of 0.35; +2 / 6 tiles gives 0.52 / 9.4% rock; +3 / 6 tiles 0.63 / 12.6%; +4 / 4 tiles 0.67 / 13.9%. Rock tracks slope closely here (it sits in the western ranges), so +3 / 4 tiles (0.58 slope, 11.2% rock) is the compromise between Switzerland's 8.8% and Britannia's 12.4%. curve: piecewise-linear [[0.0, 0.0], [458.0, 9.5], [1535.0, 19.5], [6106.0, 31.0]]. Result: mean slope 0.582 magnitude steps/tile, 11.23% rock, bands 50.0% Plains / 33.0% Highland / 17.0% Mountain, mean magnitude 10.19 (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 0.566 / 0.555, rock 10.42% / 8.96% (a coarser tile spans more ground; Switzerland 0.81 / 1.02, Britannia 0.93 / 1.25, Europe 1.18 / 1.53). Water magnitude OpenFront's convention: min(ceil(d/2), 31), d = Manhattan distance from the shoreline water. Lake policy Natural Earth lakes inside the land are lakes; a lake that reaches the border joins the sea outside it and is ocean. A lake under 40 tiles at full res (178.1 km2), 10 at 4x or 3 at 16x is filled back to land at the ground height. River policy none: rivers are not carved (at this scale they are narrower than a tile). 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 6, 16x 11. Cut-off water (mapgen_coast.py) after the lakes are cut in, each water body at full resolution that does not reach the ocean and holds no Natural Earth lake tile is either sea the DEM cut off at a strait narrower than a tile (at least 50% of it Natural Earth sea: reconnected to the ocean along Natural Earth's channel, its sea grown by one tile to bridge rasterising gaps) or ground the DEM puts at or below sea level inside Natural Earth's land (levee-protected delta islands, marsh: filled back to land). Sea bodies under 10 tiles are left to the small-lake filter. Reconnected 24 of 24 sea bodies (66 channel tiles carved); filled 38 bodies (121 tiles). 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, 550 x 347: 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 20 km (2.4 tiles of 8.44 km). Smoothed wider than the 8 km default: at 8.4 km per 16x tile, 8 km left the Koppen line between the Great Plains' steppe (BSk) and the humid east (Dfa, Cfa) along the 100th meridian a one-tile step, ruled from the Dakotas to Texas; 20 km makes it the gradual rise in rainfall it is, through a band of grass (and the terrain shader frays every class border a little). 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: BSk 24%, Cfa 23%, Dfa 18%, Dfb 12%, BWk 6%, Dfc 3%, Dsb 3%, BWh 3%, Csb 3%, BSh 2%, Csa 1%. As the temperate ladder reads it: desert 10.1%, steppe 21.2%, grass 45.0%, forest 23.7% (before the shader's noise, heat and altitude). Nations ------- One per state: the 48 contiguous states, English names; the District of Columbia (US-DC) is folded into Maryland; Alaska and Hawaii are not on the map. The spawn is the state's largest city by the 2020 US Census (population of the city proper; U.S. Census Bureau, public domain), located at its Natural Earth populated place and snapped to the nearest tile that is land at all three resolutions, in the same state and on the same landmass (coast at 16x avoided). Where Natural Earth's metro figure (POP_MAX, which picked Greece's spawns) names another city, the census city wins: Huntsville (not Birmingham), Jacksonville (Miami), Wichita (Kansas City, Kansas), Kansas City (St. Louis), Newark (Trenton), Charlotte (Raleigh), Columbus (Cleveland), Oklahoma City (Tulsa), Nashville (Memphis), Houston (Dallas), Baltimore (Washington, D.C.). The list is ordered by Natural Earth's POP_MAX of the spawn city, largest first. Flags are ISO 3166-2:US codes (us-ca ...). New York us-ny (1989, 475) New York (Natural Earth populated place, pop 19,040,000, the state's largest city, 2020 US Census) California us-ca ( 168, 822) Los Angeles (Natural Earth populated place, pop 12,500,000, the state's largest city, 2020 US Census) Illinois us-il (1445, 504) Chicago (Natural Earth populated place, pop 8,990,000, the state's largest city, 2020 US Census) Pennsylvania us-pa (1952, 524) Philadelphia (Natural Earth populated place, pop 5,492,000, the state's largest city, 2020 US Census) Georgia us-ga (1627, 912) Atlanta (Natural Earth populated place, pop 4,506,000, the state's largest city, 2020 US Census) Massachusetts us-ma (2079, 368) Boston (Natural Earth populated place, pop 4,467,000, the state's largest city, 2020 US Census) Texas us-tx (1153, 1154) Houston (Natural Earth populated place, pop 4,459,000, the state's largest city, 2020 US Census) Michigan us-mi (1623, 455) Detroit (Natural Earth populated place, pop 4,101,000, the state's largest city, 2020 US Census) Arizona us-az ( 424, 899) Phoenix (Natural Earth populated place, pop 3,551,000, the state's largest city, 2020 US Census) Washington us-wa ( 190, 85) Seattle (Natural Earth populated place, pop 3,074,000, the state's largest city, 2020 US Census) Minnesota us-mn (1226, 350) Minneapolis (Natural Earth populated place, pop 2,616,000, the state's largest city, 2020 US Census) Colorado us-co ( 762, 612) Denver (Natural Earth populated place, pop 2,313,000, the state's largest city, 2020 US Census) Maryland us-md (1902, 573) Baltimore (Natural Earth populated place, pop 2,255,000, the state's largest city, 2020 US Census) Oregon us-or ( 148, 185) Portland (Natural Earth populated place, pop 1,875,000, the state's largest city, 2020 US Census) Nevada us-nv ( 317, 735) Las Vegas (Natural Earth populated place, pop 1,823,000, the state's largest city, 2020 US Census) Virginia us-va (1951, 696) Virginia Beach (Natural Earth populated place, pop 1,491,000, the state's largest city, 2020 US Census) Missouri us-mo (1180, 662) Kansas City (Natural Earth populated place, pop 1,469,000, the state's largest city, 2020 US Census) Indiana us-in (1518, 608) Indianapolis (Natural Earth populated place, pop 1,436,000, the state's largest city, 2020 US Census) Wisconsin us-wi (1431, 440) Milwaukee (Natural Earth populated place, pop 1,388,000, the state's largest city, 2020 US Census) Rhode Island us-ri (2073, 395) Providence (Natural Earth populated place, pop 1,277,000, the state's largest city, 2020 US Census) Ohio us-oh (1643, 581) Columbus (Natural Earth populated place, pop 1,270,000, the state's largest city, 2020 US Census) Connecticut us-ct (2014, 443) Bridgeport (Natural Earth populated place, pop 1,018,000, the state's largest city, 2020 US Census) North Carolina us-nc (1769, 818) Charlotte (Natural Earth populated place, pop 995,000, the state's largest city, 2020 US Census) Florida us-fl (1773, 1079) Jacksonville (Natural Earth populated place, pop 988,000, the state's largest city, 2020 US Census) Utah us-ut ( 494, 521) Salt Lake City (Natural Earth populated place, pop 966,000, the state's largest city, 2020 US Census) Kentucky us-ky (1544, 687) Louisville (Natural Earth populated place, pop 948,000, the state's largest city, 2020 US Census) New Mexico us-nm ( 668, 850) Albuquerque (Natural Earth populated place, pop 898,642, the state's largest city, 2020 US Census) Nebraska us-ne (1123, 550) Omaha (Natural Earth populated place, pop 877,110, the state's largest city, 2020 US Census) Tennessee us-tn (1512, 800) Nashville (Natural Earth populated place, pop 877,000, the state's largest city, 2020 US Census) Oklahoma us-ok (1058, 855) Oklahoma City (Natural Earth populated place, pop 788,000, the state's largest city, 2020 US Census) Louisiana us-la (1395, 1140) New Orleans (Natural Earth populated place, pop 785,000, the state's largest city, 2020 US Census) South Carolina us-sc (1826, 938) Charleston (Natural Earth populated place, pop 411,940, the state's largest city, 2020 US Census) Kansas us-ks (1068, 736) Wichita (Natural Earth populated place, pop 401,843, the state's largest city, 2020 US Census) Iowa us-ia (1217, 530) Des Moines (Natural Earth populated place, pop 380,655, the state's largest city, 2020 US Census) Idaho us-id ( 359, 342) Boise (Natural Earth populated place, pop 338,071, the state's largest city, 2020 US Census) New Jersey us-nj (1983, 479) Newark (Natural Earth populated place, pop 280,123, the state's largest city, 2020 US Census) Arkansas us-ar (1281, 892) Little Rock (Natural Earth populated place, pop 270,893, the state's largest city, 2020 US Census) Mississippi us-ms (1381, 1016) Jackson (Natural Earth populated place, pop 250,902, the state's largest city, 2020 US Census) Alabama us-al (1527, 876) Huntsville (Natural Earth populated place, pop 212,733, the state's largest city, 2020 US Census) New Hampshire us-nh (2056, 335) Manchester (Natural Earth populated place, pop 196,566, the state's largest city, 2020 US Census) North Dakota us-nd (1095, 251) Fargo (Natural Earth populated place, pop 162,842, the state's largest city, 2020 US Census) Delaware us-de (1940, 541) Wilmington (Natural Earth populated place, pop 161,560, the state's largest city, 2020 US Census) South Dakota us-sd (1095, 427) Sioux Falls (Natural Earth populated place, pop 155,724, the state's largest city, 2020 US Census) Maine us-me (2087, 289) Portland (Natural Earth populated place, pop 135,866, the state's largest city, 2020 US Census) West Virginia us-wv (1710, 659) Charleston (Natural Earth populated place, pop 123,799, the state's largest city, 2020 US Census) Montana us-mt ( 662, 279) Billings (Natural Earth populated place, pop 104,552, the state's largest city, 2020 US Census) Vermont us-vt (1972, 275) Burlington (Natural Earth populated place, pop 93,807, the state's largest city, 2020 US Census) Wyoming us-wy ( 776, 539) Cheyenne (Natural Earth populated place, pop 72,927, the state's largest city, 2020 US Census) Lower 48 only: Alaska and Hawaii are left out (clip_lonlat drops their polygons; their admin-1 regions US-AK and US-HI are not nations). Canada, Mexico and the Bahamas are water (the Switzerland rule). The Great Lakes: Natural Earth's US polygon runs to the border in the middle of the lakes and ne_10m_lakes cuts the lakes out of it; they reach the border, join the water Canada becomes and are ocean, so boats sail them. Lake Michigan joins Lake Huron through the Straits of Mackinac (about 3 tiles wide). Lake of the Woods and Lake Champlain (which reaches Quebec) are ocean for the same reason. coast.band_from "sea": the DEM refines only the sea coast (within 3 km of Natural Earth's sea); along the land borders with Canada and Mexico every tile of the US polygon is land, so the Imperial Valley, at about sea level on the Mexican border, is not drowned. Features narrower than a tile (2.1 km) close: the East River (Long Island joins Manhattan), most of the Florida Keys (a few of the larger keys remain), the Outer Banks in places. The Columbia River estuary is land: Natural Earth draws it inside the US polygon and no lake layer has it. Rivers are not carved (the Mississippi is about 1 km wide).