Astrocartography (天星擇地)

Locational Astrology — Where on Earth Your Stars Come Alive

Overview

Astrocartography (AstroCartoGraphy, or ACG) is the art of mapping your birth chart onto the surface of the Earth. At the instant you were born the ten planets occupied fixed positions in the sky — but where on the globe each planet was rising, setting, culminating overhead, or anchored at the lowest point of the sky depends on geography. ACG draws those four 'angular' positions for every planet as lines across a world map, so you can see where Venus was on the horizon, where the Sun was at the zenith, or where Saturn was at the meridian. Living, working, or travelling near a line is said to amplify that planet's energy in the corresponding area of life — career, love, home, or self.

Origin & history

Astrocartography was created in the 1970s by the American astrologer Jim Lewis (1941–1995), who trademarked the name 'Astro*Carto*Graphy' and built the first commercial service plotting planetary lines on maps. Lewis drew on a much older idea — that a chart can be 'relocated' to any place on Earth — but his innovation was the visual map of continuous planetary lines, which made locational astrology intuitive and widely usable. His system became the standard, and the techniques were extended by later practitioners such as Martin Davis ('From Here to There') and through software like Astro Gold and astro.com.

The roots of relocation reach back to Hellenistic and medieval astrology, where charts were recast for new cities, but locational astrology as a distinct discipline is modern. Jim Lewis taught and lectured prolifically through the 1980s and early 1990s, and after his death the field split into competing software implementations that still differ slightly in convention (zodiacal vs in-mundo projection, whether to include the lunar nodes and Chiron, how wide to draw the zone of influence). askTIAN implements the classic Lewis 'in-mundo' method — lines drawn where each planet is physically on the horizon or meridian — using a Meeus-precision ephemeris, the convention against which most serious modern tools are validated.

How it works

askTIAN converts your birth date, time, and timezone offset to a single instant in Universal Time and computes Greenwich Mean Sidereal Time (GMST). For each of the ten classic bodies (Sun, Moon, Mercury through Pluto) it calculates the true geocentric right ascension and declination — crucially including each body's ecliptic latitude, since ignoring it would shift the Moon's and Pluto's lines by hundreds of miles. The MC (Midheaven) and IC (Imum Coeli) lines are straight meridians at longitude RA − GMST (and its opposite); the ASC (rising) and DSC (setting) lines are curves solved latitude-by-latitude from the horizon equation H₀ = arccos(−tan φ · tan δ), giving longitude = RA ∓ H₀ − GMST. The zodiac is tropical (no ayanamsa is applied). If you supply a birthplace, the engine reports which lines run near it under a two-tier orb — 'active' within ~700 miles and 'strong' within ~150 miles — plus a 0–100 quality score weighing benefic against challenging lines.

Good for

Use cases

Relocation Planning

Supply a birth date, exact time, timezone offset, and a candidate city's latitude and longitude. The API returns every planetary line that runs near that city — sorted by distance, flagged active (≤700 mi) or strong (≤150 mi) — with a per-line reading and an overall location-quality score, so an app can rank cities by astrological theme.

Career & Visibility Mapping

Filter the returned lines to the MC (Midheaven) angle and the Sun and Jupiter bodies to surface the places most associated with recognition, success, and public reputation — the classic 'fame and fortune' lines of locational astrology.

Love & Partnership Mapping

Surface the Venus lines and any planet on the DSC (Descendant) to highlight where relationships, attraction, and partnership are emphasised — a popular feature for travel-and-dating or 'where will I meet someone' experiences.

Travel & Lifestyle Content

Because the 40 lines (10 planets × 4 angles) are returned as map-ready longitudes and latitude/longitude polylines, content sites and apps can render an interactive world map of a user's planetary lines without any astronomy code of their own.

Key terms

Planetary line
The path on a world map where a given planet was exactly on one of the four chart angles (ASC, MC, DSC, IC) at the birth moment. Each of the ten planets has four lines, for forty in all.
MC / IC lines
The Midheaven and Imum Coeli lines — straight north–south meridians where a planet was culminating overhead (MC, career and visibility) or at the lowest point of the sky (IC, home and roots) at longitude RA − GMST and its opposite.
ASC / DSC lines
The Ascendant (rising, eastern horizon — self and vitality) and Descendant (setting, western horizon — relationships) lines. These are curves, not straight lines, because the rising/setting longitude changes with latitude.
Zone of influence (orb)
The band either side of a line within which its effect is considered active. The classic Jim Lewis figure is ~700 miles, with the strongest effect in a tight core of roughly 150 miles; influence is a gradient, strongest on the line itself.
In-mundo vs zodiacal
Two valid projection conventions. In-mundo (used here, the Lewis default) draws lines where a planet is physically on the horizon or meridian; zodiacal draws them where the planet's ecliptic longitude meets the angle. They diverge most for off-ecliptic bodies like Pluto.
Parans
Latitude bands where two planetary lines cross, so two planets are angular at once. An advanced layer of locational astrology, distinct from the forty primary lines.

API

The askTIAN Astrocartography API projects all ten natal planets onto the Earth as forty angular lines — MC/IC meridians and ASC/DSC curves — computed in-mundo from each body's exact birth-moment right ascension and declination (ecliptic latitude included, tropical zodiac). Pass a birthplace to receive a two-tier nearby-line report (active ≤700 mi, strong ≤150 mi), a 0–100 location score, and a fixed-section LLM reading. The astronomy is exact; the meanings are symbolic. Set interpretation:false for structured data only.

Endpoint: POST /trpc/astrocartography.calculate — 6 TIAN Points. See the API documentation and Playground.