China, meet
Argentina.

Turn China upside down, carry it half a world east, and its heart comes down on Argentina. Shanghai lands in Entre Ríos, 34 km from Los Charrúas; Nanjing beside Gálvez, in Santa Fe; Beijing in northern Patagonia near General Conesa, on the Río Negro; Tianjin south of Bahía Blanca. The Pearl River Delta lands high in the Andes of Jujuy: Shenzhen near Rinconada, Guangzhou near Susques, and Hong Kong 30 km from La Quiaca on the Bolivian border. Xi’an faces the Chilean countryside near Coltauco, south of Santiago, and Santiago faces the mountains of southern Shaanxi.

Taiwan sits on the Gran Chaco: Taipei 11 km from El Espinillo in Formosa province, Kaohsiung and Tainan on the Mennonite colonies of the Paraguayan Chaco around Loma Plata and Colonia Neuland. Mongolia lands in Patagonia: Ulaanbaatar near Cochrane in Chilean Aysén, and the towns of the Mongolian steppe on the Patagonian steppe of Santa Cruz and Chubut. Siberia comes down at the tip of the continent: Ulan-Ude is 13 km from Puerto Natales, Punta Arenas faces the eastern shore of Lake Baikal, and Ushuaia the Barguzin valley beyond it. Even the Falklands have a twin, in the forests of the Greater Khingan in Inner Mongolia.

What misses is the north-east and the south-west. Harbin, Changchun and Shenyang face the South Atlantic off Argentina, like the Russian Far East; Chengdu, Chongqing and Kunming face the Pacific off Chile. Buenos Aires itself falls just short: its antipode is in the Yellow Sea, 126 km from the coast of China, which makes a sloppy sandwich, and an exact one 126 km inland near Carmen de Areco. And La Paz lands in the South China Sea, 12 km from the Paracel Islands.

Every Chinese city above three million people and every provincial capital in the east; the cities of Taiwan above 250,000, Hong Kong and Macau; every Mongolian provincial centre; the larger cities of southern Siberia. On the other side, every Argentine and Chilean city above 100,000 and every provincial or regional capital, and the cities of Paraguay, Uruguay and Bolivia whose other slice lands in or off China, Mongolia or Siberia. Exact means land opposite land at the city’s own point; where the other slice would get wet, the table gives the nearest spot from which an exact sandwich is possible. Every place links to the map.

Some towns have a twin: another town whose centre is less than a kilometre from their exact antipode. Put bread in the middle of each and you have an exact Earth sandwich without leaving either town. This corridor has three, and two of them are big cities: Hefei, the capital of Anhui, is 725 m from the antipode of Las Varillas in Córdoba province, and Wuhan, the capital of Hubei, 760 m from Castro Barros in La Rioja.

1. Las VarillasCordoba⇄HefeiAnhui725 m
2. Castro BarrosLa Rioja⇄WuhanHubei760 m
3. San LorenzoCorrientes⇄ZhugangZhejiang807 m

Distances are between the centre points GeoNames gives for each town. Sandwich Law measures from where the bread actually lies, plus both phones’ GPS accuracy, so check your two spots on the map before the day.

A sandwich’s elevation bonus is the height of one end plus the height of the other (Sandwich Law § 1.4). The Board scores it the way the map shows it: from the average height of the ground over cells about 20 km across, so every spot in a cell scores the same and you only need to be in the right cell, not on the summit. These are the corridor’s best cells, one per area, each with dry land at both ends.

1. +6,160 m35 km from Rongmei (Hubei)cell average 1,560 m54 km from Las Flores (San Juan)cell average 4,600 m
2. +6,080 m16 km from Dangyang (Chongqing)cell average 1,800 m44 km from Barreal (San Juan)cell average 4,280 m
3. +5,840 m26 km from Shuiche (Hunan)cell average 520 m117 km from Vinchina (La Rioja)cell average 5,320 m
4. +5,840 m16 km from Shaoyang (Hunan)cell average 280 m78 km from Palo Blanco (Catamarca)cell average 5,560 m
5. +5,440 m25 km from Fuchuan (Guangxi)cell average 600 m187 km from Antofagasta de la Sierra (Catamarca)cell average 4,840 m

The mountains of western Hubei lie opposite the high Andes of San Juan, and that puts this corridor second on Earth: the best cell averages 1,560 m on the Chinese side and 4,600 m on the Argentine. Only a pair between Vietnam and Peru scores higher (see that guide). The Argentine ends are high Andean desert: plan for altitude and cold before anything else.

The window. Both slices must go down within five minutes of the same UTC instant (Sandwich Law § 2.1). The sandwich lobby holds you to it: when the first slice lands, the other side has five minutes.

The clocks. China, Taiwan, Hong Kong and Mongolia keep one time, UTC+8, all year, and Argentina and Paraguay keep UTC−3: Buenos Aires is always 11 hours behind Beijing. Chile moves its clocks, so it is 11 hours behind China from September to April and 12 hours behind from April to September.

The light. Two exactly opposite points are never in daylight together: sunrise at one end is sunset at the other. The atmosphere bends a little sunlight over the horizon, though, so twice a day, on a clear flat horizon, the sun is up at both ends at once for eight to ten minutes at these latitudes, a little longer in Patagonia and by Lake Baikal. Put the bread down then and both photographs get golden light, one at dusk and one at dawn.

The seasons. Opposite too: the Chinese New Year falls in the Argentine summer, and a Beijing winter is a Patagonian summer.

The geometry is the easy part; the hard part is a person at the other end, and the site does not match strangers. The two sides do not share a language, so write in both: Spanish and Chinese, or Spanish and Mongolian, with your town and its antipode. Buenos Aires has a Chinatown, the Barrio Chino in Belgrano, and there are Chinese and Taiwanese communities in Argentina and Paraguay, which is where many sandwiches between these countries will start.

Then open an attempt in the sandwich lobby. It gives you a code and a link to send through whatever channel you already share, shows both slices when they arrive, and runs the five-minute window. Much of the Argentine side is estancia land and much of the Andean side is remote and high, so put the bread on public ground, a roadside, a square or a park, or ask whoever owns the field. The exact grade allows a kilometre of slack, which is usually enough to find somewhere you are allowed to stand.

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