Map Tunnel — Where Would You Come Out?
If you dug a perfectly straight tunnel through the Earth, where would you emerge? Two globes side by side, synchronised in real time. Pan or rotate the left one and the right one rotates to your antipode — the exact opposite point on the planet. Search a city, tap Detect My Location, or click anywhere on the left globe to start the tunnel.
The Map Tunnel is a dual-globe antipode visualiser. The left globe is the entry — where the tunnel begins — and the right globe is the exit, the point on Earth's surface diametrically opposite the entry. Both views are real OpenStreetMap data rendered as 3D globes, and they stay mathematically locked: drag one and the other rotates in mirror in real time, so you can sweep across a continent and watch the opposite side of the planet trace out as you go. Below the maps the tool reads back the country or ocean at each end, your hemisphere, the chord through Earth's core (a constant 12,742 km), the great-circle distance over the surface (a constant 20,037 km), and the 12-hour solar-time flip between the two ends. Most tunnels — about 95% of them— emerge in open ocean. The fun is finding the rare pairs that don't.
What is a tunnel through Earth, really?
A "tunnel through the Earth" is shorthand for the line that connects any point on the surface to its antipode — the point on the opposite side of the planet, passing through the centre. For any point at latitude φ and longitude λ, the antipode is at (-φ, λ ± 180°). Latitude flips sign (north becomes south); longitude shifts by exactly half the world (east becomes west or vice versa).
The tunnel itself, if it could be drilled, would be exactly 12,742 km long — the mean diameter of the Earth. Around the surface, the great-circle distance between any antipode pair is 20,037 km — exactly half the equatorial circumference. Both numbers are constants: they do not change with where you start.
What does change is what you find at the other end. The Earth is about 71% ocean, so most tunnels emerge in open water. Only about 4–5% of land has its antipode also on land. The Map Tunnel makes that statistic visible: drag the left globe across the United States and the right globe sweeps across blank ocean; drag it across central China and the right globe traces a clean line across Argentina.
How to use the Map Tunnel
Five simple paths — pick whichever fits your context.
- Pick your starting point. Type a city, address, or landmark in the search box; tap the GPS button to use your current location; or click anywhere on the left globe. The left pane is the entry — where you start digging.
- Watch the right globe rotate to your antipode. The right globe — the exit — instantly rotates to the antipode (the point exactly opposite on Earth). The two globes stay synchronised: drag one and the other follows in mirror, so you can rotate the planet and watch the tunnel emerge anywhere.
- Read the through-Earth and around-Earth distances. Below the maps the panel shows the chord through Earth (a constant 12,742 km / 7,918 mi — the diameter), the great-circle distance over the surface (20,037 km / 12,451 mi — half the equatorial circumference), and the time-of-day flip on the opposite side.
- Click the right globe to invert the tunnel. Clicking the antipode globe sets the entry to the antipode of where you clicked — the inverse direction. Useful for asking "if someone dug through to me, where would they have started?"
- Swap, reset, or copy the coordinates. Use Swap to mirror entry and exit. Use Reset to clear and start over. The entry and exit coordinates are shown in standard decimal-degrees format below each globe.
What people use the Map Tunnel for
Six recurring patterns we see in the analytics.
Answer the kid question — "where would I come out if I dug to the other side?"
It is the oldest geography question on Earth. The answer is almost never "China" — for most of the United States the tunnel emerges in the southern Indian Ocean, somewhere between Madagascar and Western Australia. The dual-globe view makes the answer obvious in one glance: the entry on the left, the exit on the right, both visible at once.
Side-by-side antipode comparison for geography lessons
A common classroom exercise — compare a country to its antipode. The Map Tunnel shows both at the same scale on synchronised globes, so a student can see at once that Spain and New Zealand cover similar latitudes, that East Asia and southern South America are almost mirrored, and that most of the world is mostly water on the opposite side.
Visualise the China–Argentina antipodal corridor
The largest connected land-to-land antipodal region on Earth is China–Mongolia opposite Argentina–Chile. Drag the left globe across central China and the right globe traces a clean ribbon across the Argentine pampas — one of the few cases where digging through really does come out on land.
Plan an antipodal travel theme — circumnavigation halfway points
For round-the-world sailors and pilots, the antipode is the natural midway turn-around — the point exactly halfway in any direction. The Map Tunnel gives an at-a-glance view of "where am I, where is my halfway point, what does it look like there?" — useful for picking a meaningful stopover or a yacht-race waypoint.
Curiosity content for blogs, social, and travel writing
Travel bloggers, photographers, and meme accounts use through-Earth views for "you are now standing exactly opposite of X" content. The dual-globe screenshot is more visually striking than a single-map antipode marker — it shows both ends of the tunnel as actual places, not just coordinates.
Test geographic intuitions — most of them are wrong
Almost every country-to-country antipode myth is incorrect. The UK is not opposite Australia; New York is not opposite China; the United States is not opposite Russia. The Map Tunnel puts the real answer in front of you in two seconds — usually open ocean, occasionally a surprise like Hawaii ↔ Botswana or Bermuda ↔ Western Australia.
Famous tunnel pairs — what is on the opposite side?
A reference of well-known cities and what lies on the other side of the planet. Most tunnels emerge in ocean, which is why the few land-to-land pairs are famous.
| Entry (your side) | Exit (other side) | Note |
|---|---|---|
| New York City, USA | Indian Ocean (≈300 mi SW of Augusta, Western Australia) | The "tunnel to China" myth — actually the southern Indian Ocean. |
| Beijing, China | Argentina (≈40 mi NE of Bahía Blanca) | The most famous true land-to-land tunnel pair in the world. |
| Madrid, Spain | Weber, New Zealand (Hawke’s Bay region, North Island) | The canonical Europe ↔ Oceania tunnel pair. |
| Auckland, New Zealand | Seville region, Spain (near Marchena) | Mirror of the Madrid → NZ tunnel. |
| Tokyo, Japan | South Atlantic (≈2,000 km E of Buenos Aires) | Japanese tunnels exit deep in the South Atlantic. |
| London, UK | Pacific Ocean (≈700 km SE of New Zealand) | British tunnels emerge in the deep Pacific — far from any land. |
| Honolulu, Hawaii | Botswana ↔ South Africa border region | A rare US-state-to-Africa tunnel — through Earth onto solid land. |
| Buenos Aires, Argentina | Eastern China (Shanghai region) | Mirror of Beijing → Argentina — a tunnel that crosses two megacities. |
| Bermuda | Western Australia (Perth region) | A North-Atlantic-to-Indian-Ocean coast tunnel. |
| Lima, Peru | Hanoi, Vietnam region (≈600 km off true) | A near-antipode pair — Lima and Hanoi are almost on opposite sides. |
| Reykjavík, Iceland | Antarctic Ocean (≈SE of Australian Antarctic Territory) | Far north tunnels emerge in far southern waters near Antarctica. |
| Christchurch, New Zealand | A Coruña region, Spain | Two cities very close to true antipodes — within ~100 km. |
The numbers behind the tunnel
Every value displayed in the result panel comes from a small set of Earth-shape and Earth-interior constants. The numbers below are the basis of every figure in the tool.
| Quantity | Value | Source |
|---|---|---|
| Distance through Earth (chord, mean diameter) | 12,742 km / 7,918 mi | IUGG mean radius × 2 |
| Distance around Earth — surface, antipode pair | 20,037 km / 12,451 mi | π × mean radius |
| Time-of-day flip at the antipode | Exactly 12 h difference (UTC offsets always sum to ±24 h) | Spherical-Earth geometry |
| Earth’s mean radius (volumetric) | 6,371 km / 3,959 mi | IUGG 1980 |
| Earth’s surface that is ocean | ≈ 71% | NOAA / NASA |
| Probability a random tunnel exits on land | ≈ 4–5% (29% × 29% × correlation adjustment) | Empirical (most land has ocean antipodes) |
| Hottest point along the tunnel | Inner core: ≈ 5,200 °C (≈ Sun surface) | Seismology, Dziewonski–Anderson PREM |
| Pressure at Earth’s centre | ≈ 360 GPa (≈ 3.6 million atmospheres) | PREM, USGS |
The physics of a hypothetical tunnel
1. Could it actually be drilled?
No, not with anything resembling current technology, and probably not ever. The tunnel would pass through the Earth’s mantle (1,000–2,500 °C), the outer core (liquid iron at 4,000–5,400 °C), and the inner core (5,200 °C, solid iron under 360 GPa pressure — about 3.6 million atmospheres). The deepest borehole ever drilled — the Kola Superdeep Borehole — reached 12,262 metres, which is 0.19% of the way to the centre. The borehole was abandoned because at 180 °C the rock behaved more like plastic than rock and the drill bit kept getting stuck.
2. The gravity-tunnel problem
In the classical physics problem (frictionless, airless, uniform Earth), an object dropped into a straight tunnel between antipodes oscillates back and forth like a pendulum. The half-period — the time to "fall" from one side to the other — is approximately 42 minutes 12 seconds, regardless of which two antipodes you connect. At the centre the object would be moving at about 7.9 km/s— roughly the orbital velocity at the Earth’s surface — and the gravity would be zero (all directions of mass cancel).
3. Why all tunnels take the same time
It is a beautiful result of simple harmonic motion: in a uniform-density Earth, the time to fall through any straight chord — not just the diameter — is the same. A tunnel from New York to Beijing (chord of about 11,000 km) takes the same 42 minutes as a tunnel from New York to its true antipode in Western Australia. This is the basis of theoretical "gravity train" proposals from the 19th century onwards.
4. The Coriolis problem
A real Earth-tunnel object would not fall straight down because the Earth is rotating. At the equator the surface moves east at about 1,670 km/h, while at depth the rotational speed is lower. An object dropped into a vertical tunnel would press against the eastern wall on the way down — a mile of horizontal drift over a 6,371-km depth. This is why gravity-tunnel proposals always assume a thought-experiment Earth: non-rotating, uniform, airless.
Why most tunnels emerge in ocean — the 71% rule
Earth’s surface is roughly 71% ocean. If land were uniformly distributed, the probability that a random point and its antipode are both on land would be about 8.4% (29% × 29%). Empirically the figure is even lower — about 4–5% — because landmasses are correlated: most land is concentrated in the northern hemisphere, with large oceans (Pacific, southern Indian, southern Atlantic) on the opposite side.
The major land-to-land tunnel corridors are:
- East Asia ↔ South America. Most of central and western China, plus parts of Mongolia and Tibet, sit opposite Argentina, Chile, and parts of Bolivia. This is the largest connected land-to-land antipodal region — which is why "if you dig a hole in China you come out in Argentina" is approximately true.
- Iberian Peninsula ↔ New Zealand.Spain and Portugal are roughly opposite New Zealand’s North and South Islands. Hamilton, NZ is close to Córdoba, Spain; Christchurch is close to A Coruña region.
- Southeast Asia ↔ Northern South America. Parts of Borneo, Malaysia, and Indonesia overlap with Colombia, Ecuador, and Peru — though both regions straddle the equator with significant ocean coverage.
- Hawaii ↔ Botswana. The Hawaiian Islands are roughly opposite the Botswana / Namibia / South Africa border region — a rare US-state-to-Africa pair.
- Greenland ↔ Antarctica. Far north opposite far south — one ice continent for another.
Map Tunnel vs Antipode Finder — when to use which
Both tools answer the same underlying question. The choice depends on what you want to see.
- Map Tunnel (this tool) — two side-by-side globes, synchronised. Best for visual comparison, lessons, and content where the "two real places at the same scale" framing matters. Drag-sync makes it easy to sweep a region and watch the opposite side trace out in real time.
- Antipode Finder — single map with both pins. Best for one-shot lookup, sharing a screenshot of a specific antipode pair, or copying coordinates in DD / DMS / DDM with country and ocean metadata.
The word "antipode" — etymology and history
"Antipode" comes from the Greek antípodes — literally "feet opposite", from antí (opposite, against) and poús (foot). In ancient Greek geography, the antipodes were thought to be a hypothetical race of people living on the other side of the spherical Earth, "with their feet against ours". The word entered English in the 14th century with the same meaning.
Capitalised, "the Antipodes"is a colloquial British term for Australia and New Zealand — because they are roughly antipodal to the British Isles. Geographically the term is loose: London’s actual antipode is in the South Pacific, not in New Zealand. But the historical association is firm enough that "Antipodes" remains a common shorthand for the region.
Related tools and resources
For a single-map antipode lookup with country and ocean metadata: Antipode Finder. For the great-circle distance between any two specific points (not just antipodes): Distance Between Two Places. For the geographic midpoint between two locations (the opposite of an antipode pair): Halfway Between Two Places. For converting the antipode coordinates into DMS, DDM, UTM, or Plus Codes: GPS Coordinate Converter. To find the latitude and longitude of any place: Latitude & Longitude Finder. To see the day-night terminator and where it currently is on Earth: Day Night Map.
Frequently asked questions
Antipode math: arithmetic on the spherical Earth model — antipode of (φ, λ) is (-φ, λ ± 180°), with longitudes wrapped into the ±180° range. Distance constants: IUGG mean Earth radius 6,371 km, mean diameter 12,742 km, half-circumference π × R = 20,037.5 km. Earth-interior temperature and pressure figures: PREM (Preliminary Reference Earth Model, Dziewonski & Anderson 1981), USGS, IRIS. Gravity-tunnel half-period (42 min 12 s) derived from simple-harmonic-motion analysis of a uniform-density Earth. Place names: Photon reverse-geocode (OpenStreetMap-derived). Map basemap and globe rendering: OpenFreeMap Liberty vector tiles via MapLibre GL JS globe projection. All data is public-domain or permissively licensed; no API keys, no rate limits, no data leaves your browser beyond the optional Photon enrichment query.
More SimpleMapLab tools
Single-map antipode lookup with country, ocean, and distance through Earth.
Measure the great-circle distance between any two points on Earth.
See the live terminator and where it is currently day or night on Earth.
Find the centroid of any country or US state on a globe.