Antigea answers one question — what is on the exact opposite side of the Earth from you? — and this page documents exactly how, because a tool you cannot interrogate is a tool you should not trust.
Your address is geocoded with Nominatim, the search engine built on OpenStreetMap data. Nothing is stored: the query goes out, coordinates come back. The same OSM data powers the autocomplete suggestions as you type.
The antipode itself is pure arithmetic, two operations: latitude changes sign, longitude shifts by 180°. No projection tricks, no approximation — the antipode of (lat, lng) is exactly (−lat, lng ± 180°).
Here is where honesty matters. For most searches the exact antipode is open ocean, and a tool that silently teleports you to the "nearest city" would be lying about the distances involved. Antigea instead runs an expanding search for the nearest official Google Street View coverage — checking a 25 km radius, then 100, 500, 1,500, out to a 3,000 km cap. Results are validated two ways: user-uploaded photo spheres are rejected (only official coverage counts, otherwise ocean antipodes surface someone's boat photos), and any panorama further away than the radius we asked for is discarded — Google's metadata service occasionally returns bizarre far-away matches, and we once received a Lisbon wine shop as the "nearest" view for a point in the Antarctic ocean.
If nothing survives within 3,000 km, the site says so plainly: remote open ocean, no Street View, nothing for thousands of kilometres. Some antipodes — like Moscow's, out near Point Nemo — deserve that honesty.
Coordinates become human-readable places through reverse geocoding — Nominatim again for the live app. For our city antipode pages, the nearest-land facts were precomputed with Komoot's Photon geocoder and then filtered, because raw geocoding data cheerfully returns seas, timezone boundaries, shipwrecks and marine reserves as the "nearest feature." Every published fact — "Madrid's antipode is 1 km from a New Zealand hilltop" — refers to a real, named, on-land place, with the measured distance beside it.
Distances use the haversine formula on a spherical Earth (accurate to well under 1% for this purpose — the real planet is about 0.3% flattened). Local time at the antipode comes from the destination's actual political timezone, not the crude 12-hour flip. Maps and Street View panes are Google Maps embeds; the guessing maps are Leaflet with CARTO tiles over OSM data. The daily game picks its city from a fixed rota, so everyone in the world gets the same puzzle on the same day — that is what makes the shareable result grid comparable between friends.
Found something that looks wrong? Email [email protected] — a correction improves the map for everyone.