The same recorded 3:30 p.m. in Liaoyang, Urumqi, London or New York does not identify the same UTC instant or solar position. A reproducible chart needs the city, coordinates, IANA time zone and the offset actually in force on that date.
Why the city matters, not just the country
Countries often contain multiple time zones, and regions may have changed zones historically. City search provides coordinates and a specific time-zone identifier; the system then queries rules for the birth date. Users are not expected to remember whether daylight saving applied in that year.
Coordinates also drive true solar time. Two cities can share a civil zone yet require different longitude corrections when they are far apart east to west.
Historical time-zone data has limits
Modern time-zone records are comparatively complete; older periods and some regions may retain only approximate history. A calculation should record its data version and confidence, and disclose insufficient history rather than pretend minute-level precision.
If a birth record gives only a province, rural area or renamed city, select the nearest place with matching time-zone history and keep an approximation note. More exact coordinates matter when the difference could cross a pillar boundary.
What if the birth time is approximate
When a time is marked approximate, the answer is not to generate twelve charts and let the user choose. The system should test a reasonable range around the input for an Hour, Day, Month or Year boundary. If none is crossed, the main structure is usually stable; if one is crossed, conclusions depending on that pillar receive lower confidence and both possibilities are disclosed.
When the hour is entirely unknown, the system should not invent noon or reverse-engineer certainty from life events. A limited three-pillar analysis can be offered while omitting conclusions that require the Hour Pillar.