How your map is calculated
Your birth moment determines the geometry. Themes help you explore it. Here is what the map calculates, what the city list shows, and where interpretation begins.
Start with an actual birth moment
Enter a birth date, accurate local time and birth city. The city supplies a named time zone, which Temporal uses to turn the local clock time into a UTC instant. The supported local birth year starts at 1900; future birth moments are rejected.
The calculator rejects invalid dates and clock times that are missing or repeated during a daylight-saving change. If your birth time is unknown, it does not silently substitute noon. Historical time-zone rules depend on the database supplied by your browser or runtime, so not every historical place and date has been independently verified.
From the sky to the map
Astronomy Engine calculates geocentric apparent positions for the Sun, Moon, Mercury, Venus, Mars, Jupiter and Saturn. The engine computes four angular lines for each body: upper meridian (MC), lower meridian (IC), rising (ASC) and setting (DSC).
Rising and setting lines use the body’s center and a geometric horizon, without atmospheric refraction or topocentric parallax. This implementation does not include outer planets, lunar nodes, parans, transits or a relocated natal chart. Other tools may use different definitions or settings.
What the themes actually show
The engine computes 28 lines, but this interface deliberately uses six of them. Career & expression uses Sun MC, Mercury MC and Saturn MC. Love & connection uses Venus DSC. Learning & growth uses Jupiter ASC. Home & belonging uses Moon IC.
All themes means the union of those six theme lines, not all 28 calculated lines. These theme choices and the short activity prompts are symbolic interpretation rules, not evidence of likely career, relationship or relocation outcomes.
Why a city appears in your results
Cities are ordered by the shortest spherical distance to the active theme lines, using a mean Earth radius of 6,371.0088 km. The list shows the first six matches from the supplied destination set, filtered to cities with a population of at least 100,000. It is not a search across every city in the world.
A smaller distance describes geometry, not a stronger effect, a luck score or a better place to live. The birthplace search catalogue is separate from the destination set. The local HTML report preserves the selected theme’s city results and explanations; it is not a PDF or a full natal-chart reading.
A reproducible example
The initial map is labelled as an example. It uses the teaching input 15 June 1995, 09:30 in Shanghai (Asia/Shanghai), not a customer’s personal story. Open the map, select Learning & growth, and inspect a city: its matched line is Jupiter ASC because that is the theme’s stated rule.
Change the time and generate the map again to compare the resulting geometry. Editing a field alone does not change the existing result; the pending notice remains until you calculate again. An example demonstrates how the tool works, not whether an astrological interpretation predicts someone’s life.
Validation and corrections
The project’s calculation tests cover input and time-zone errors, angular-line geometry, map boundaries and distance ordering. A development comparison on 9 September 2026 used Swiss Ephemeris at one fixed instant, 1 January 2000 at 12:00 UTC. That limited check is not proof of matching every other tool or every supported date. The production engine is Astronomy Engine, not Swiss Ephemeris.
Astrological interpretation has no scientifically established predictive validity. Use the map for exploration alongside practical considerations. To report a technical problem, tell us the browser, the operation and what you expected; you do not need to email your birth details.