Astrocartography Accuracy: How Exact Is This Map?

From birth details to a line

1. Birth moment. Your local birth time is converted to universal time using the time zone history of your birthplace, including past daylight saving rules.
2. Positions in the sky. Planet positions come from astronomy-engine, an open astronomy library, with corrections from NASA JPL Horizons data for the Earth, Jupiter, Saturn, Uranus and Neptune; Pluto and Chiron come straight from JPL Horizons tables.
3. Four lines per body. For each of the 12 bodies, the map finds where on Earth it was rising, setting, at its highest point and at its lowest point at that moment. The Earth is treated as a sphere.
4. Distance to a place. The distance from a city to a line is the shortest great-circle distance, the route you would measure on a globe.

What our tests found

We compared results with Swiss Ephemeris, a standard reference in astrology software, in a test run dated November 7, 2026.

Test	Size	Result
Distance from a city to a map line	3,001 moments, 52 lines (our 48 plus the four for the mean node, which the map does not draw), 7 cities	Largest difference 0.633 km
Sun through Pluto falling in the right zodiac sign	24,002 moments	No wrong signs
True North Node falling in the right zodiac sign	24,002 moments	One wrong sign, in 2066, right on a sign boundary

That 0.633 km is far smaller than a city. Agreement with a reference does not prove a line means anything, though. It shows only that the astronomy is computed correctly.

What actually moves your lines

Here are the things that change a line, biggest effect first in everyday use.

• Birth time. The Earth turns one degree every four minutes, and one degree is about 111 km at the equator. A birth time rounded by 15 minutes can move every line by nearly four times that.
• Time zone errors. Older birth years often used different daylight saving rules, and a one-hour slip moves everything. For Maya, born in New York at 2:30 pm on June 10, 1990, moving the time one hour later, to 3:30 pm, changes the first city from Tbilisi to Istanbul.
• Drawing method. In mundo follows the body's real position in the sky. Zodiacal uses only its degree along the zodiac. On our sample map the gap is none for the Sun and the North Node, usually under about 300 km for the Moon through Mars, and more than 1,000 km in places for Pluto.
• The calculation itself. On the test above, at most 0.633 km.

When two sites disagree, check those in order. Most of the time, you will find the cause in the first three.

How a city gets its score

For each goal, the score adds up every line within 1,000 km of the city. Each line's score is:

body weight × angle weight × distance fade

Distance fade is exp(-(km/350)²). In plain terms, a line through the city counts in full, and it fades quickly as you move away.

Distance	Share counted
0 km	100%
100 km	92%
175 km	78%
350 km	37%
700 km	2%
Over 1,000 km	Not counted

Body weights

Body	Love	Career	Home
Sun	0.3	0.8	0.3
Moon	0.5	0.1	1
Mercury	0.1	0.45	0.1
Venus	1	0.2	0.6
Mars	0.25	0.4	-0.6
Jupiter	0.45	1	0.7
Saturn	-0.6	0.35	-0.4
Uranus	-0.2	0.1	-0.5
Neptune	-0.2	-0.2	-0.25
Pluto	-0.5	-0.1	-0.6
North Node	0.2	0.25	0.15
Chiron	-0.2	-0.15	-0.2

Angle weights

Line	Love	Career	Home
Rising (AS)	1	0.8	0.8
Setting (DS)	1.2	0.5	0.6
Overhead (MC)	0.5	1.3	0.3
Underfoot (IC)	0.7	0.3	1.3

The balanced goal is the average of love, career and home. When sorting, each city also gets a small lift for being well known, at most 0.6, based on how many languages have a name for it. That keeps first places among cities people really consider.

These weights are our own, set by us with astrological tradition as the guide. They are not measurements, and a different astrologer could reasonably choose others. We publish them so you can disagree with specifics.

A worked score

Maya's love score for Tbilisi, first three lines:

• Venus underfoot, 18 km: 1 × 0.7 × 0.997 = 0.70
• Moon rising, 22 km: 0.5 × 1 × 0.996 = 0.50
• Jupiter setting, 214 km: 0.45 × 1.2 × 0.688 = 0.37

Five further lines between 377 km and 745 km take a little away, and the eight together come to 1.28.

Which cities get ranked

City data comes from GeoNames, licensed under CC BY 4.0, with about 226,000 places. Candidates for the rankings number about 400: big or widely known cities and a list of long-stay destinations. Places under the US State Department's top advisory, Level 4 (data of November 7, 2026), and Western Sahara are left out. Of two cities less than 250 km apart, only the higher one stays, and a country holds at most two. Above 62° latitude, only capitals are candidates. A city must also score above zero for a goal, before the small fame lift, to make that goal's list. You can still look up any place in the database by hand.

Time ranges and parans. In Map options you can say how sure you are of your birth time. The bands shift each line east and west by the turn of the Earth over that time, 15° an hour, and ignore the slow movement of the planets themselves. Parans are the latitudes where two highlighted planets reach their lines at the same moment. We solve for the latitude from each planet's position and test that the two lines really meet there.

What a line can and cannot prove

The calculation is astronomy. The meanings are a symbolic tradition, and nothing scientific shows that living near a line changes anything in your life. We write "astrologers connect this with" because that is exactly what we can stand behind. Use the map as a prompt for thinking about places, and judge the result against your own experience.