DMS ↔ Decimal Degrees Converter

Babylonian inheritance via Greek astronomy: Ptolemy divided circles into 360 degrees, each into 60 partes minutae primae (first small parts — 'minutes'), each into partes minutae secundae ('seconds'). Sixty divides cleanly by 2,3,4,5,6,10,12 — gold for hand calculation. Navigation kept it because charts and sextants were graduated that way, and one arc-minute of latitude became the nautical mile, welding the format to an entire measurement culture. Decimal degrees are simply the same angle with the costume off.

Each DD decimal is a 10× zoom: 1 decimal ≈ 11 km (a city), 2 ≈ 1.1 km (a neighborhood), 3 ≈ 110 m (a street), 4 ≈ 11 m (a building), 5 ≈ 1.1 m (a doorway), 6 ≈ 11 cm (survey-adjacent). Publishing 8+ decimals from a phone GPS is false precision theater — consumer receivers honestly deliver 3–5 m. In DMS terms: one arc-second is ~31 m of latitude, so seconds-with-one-decimal matches a good handheld fix.

The compromise child: degrees stay whole, minutes carry decimals, seconds are abolished — 40° 26.767′. It's the default display on marine chartplotters and aviation GPS because paper-chart latitude scales are graduated in minutes (each = 1 NM), so a position in DDM reads straight onto the chart edge with dividers. Geocaching adopted it from handheld GPS culture. The double-conversion through DDM is where transcription errors breed; this tool shows all three formats simultaneously to short-circuit that.

The classic failure modes: a dropped minus sign (S/W hemispheres are negative in DD — 'they're for Australia what the N is for Norway'); lat/long swapped (Google Maps URLs are lat,lon; GeoJSON is [lon, lat] — the single most common GIS bug); DMS punctuation parsed as decimals (40.2646 from 40°26′46″ is ~2 km off — note it's not even close to 40.4461); and locale commas read as decimal points. When a point lands in the ocean off West Africa, that's (0,0) — the null island where lost coordinates go to die.