How Accurate Is Astrocartography? An Honest Answer

“How accurate is astrocartography?” is really two questions. The first is whether the lines are drawn in the right place. That can be checked, and for a given birth time and place the answer is yes: it is astronomy. The second is whether a line says anything true about a place. That cannot be tested the same way, and there is no scientific evidence that it does. Keeping the two apart is the honest way to use a map.

What can be checked: where the lines are

Every line on an astrocartography map marks the places where a planet was rising, setting, overhead or underfoot at a given moment. Where those places are is a calculation, not an opinion. ElevenMaps takes planet positions from DE440, the ephemeris of NASA’s Jet Propulsion Laboratory, through the open-source Skyfield library. Automated tests then compare every one of the 40 lines with a second calculation that reaches the answer by a different route. The one known gap is the Moon, which is so close to Earth that the two methods can differ by about a degree because of parallax. Our method page lists every step.

What moves a line: your birth data

A line is only as accurate as the birth data behind it, and the birth time matters most. The Earth turns 15 degrees of longitude an hour, so the lines move with it. At the latitude of Lisbon, one hour is about 1,303 km on the ground and ten minutes is about 217 km. On our example chart (Casablanca, 14 May 1992, 12:00) the Venus MC line passes 25 km from Lisbon. Shift the birth time by ten minutes and the picture changes:

• Born at 11:50: Lisbon is 242 km from the line.
• Born at 12:00: Lisbon is 25 km from the line.
• Born at 12:10: Lisbon is 192 km from the line.

The birth place matters too, but mostly for a quiet reason: it tells us which clock and which time-zone rules applied, so that local time can be turned into universal time. A wrong time zone is an error of a whole hour or more. Our guide do you need your birth time for astrocartography? covers what to do when you only know it roughly.

How far a line reaches: a rule, not a measurement

A line is a thin curve, but a place does not have to sit exactly on it to be “on the line”. How far a line reaches is a convention, and astrologers disagree about it. ElevenMaps counts a line fully within 150 km and fades it in a straight line to nothing at 700 km. On our example chart Madrid is 437 km from the Venus MC line, so it gets about 48 per cent of the line’s weight.

That fade is our choice, written down so you can see it. It is not a law of nature, and another reader may draw the line somewhere else. This is why we talk about themes that are stronger or weaker, never about guarantees.

What cannot be checked: what a line means

Whether a Venus line makes a place feel like Venus is a claim about people, not about planets, and it has to be tested on people. The best-known double-blind test of astrology, by Shawn Carlson in Nature in 1985, found that astrologers could not match natal charts to personality profiles better than chance, although researchers still argue about how to read that result. We know of no controlled test of astrocartography itself. So we do not tell you that a line will do anything. We call every result a place to explore, for insight and reflection.

How to use a map accurately

• Use the most exact birth time you can find, and treat a rounded time (“around noon”) as approximate.
• Read “on the line” as within about 150 km, and weaker the further out you go.
• Treat each line as a theme, then test the place against real facts: cost, language, work, visas and people.
• Compare two or three places rather than looking for one right answer.

For a reading of every line on your chart, see the full astrocartography report.

Frequently asked questions

Is astrocartography accurate?

The lines are accurate astronomy for the birth data you give. What the lines mean is interpretation, and there is no scientific evidence that it predicts how a place will feel or what will happen there.

How accurate does my birth time need to be?

Closer is better. Ten minutes moves a line by about 217 km at the latitude of Lisbon, and an hour by about 1,303 km. Without a time, ElevenMaps uses local noon and marks the lines as approximate.

Why does my map look different on another site?

Sites differ in how they turn local time into universal time, which ephemeris they use, and which lines they draw. Many add extra lines such as aspect lines and parans. ElevenMaps draws the 40 core lines: ten planets, four angles each.

Can astrocartography predict my future?

No. It describes themes you may want to explore, not events that will happen. It is not medical, legal, financial or immigration advice.

Written by the ElevenMaps team. For insight and reflection.