A chart redrawn as a map
Your birth chart records where the planets were at one instant, from one place. Astrocartography asks a different question of the same instant: from every other point on Earth, how would the sky have looked? Wherever the Moon would have been exactly on the horizon or exactly on the meridian, a line is drawn.
Jim Lewis built the method in the 1970s and gave it its name. It is a modern technique, and no ancient source contains anything like it. What it borrows from older astrology is the rule that a planet on an angle carries more weight than one buried in the middle of a house.
Why two of the lines bend
The Moon MC line marks longitudes where the Moon was culminating, high on the meridian. The IC line marks where it sat at the lowest point, on the meridian below the horizon. Because a meridian is a fixed circle running pole to pole, both appear on the map as straight vertical lines.
The AC line marks where the Moon was rising on the eastern horizon, and the DC line where it was setting in the west. These curve. The angle between the horizon and the ecliptic depends on latitude, so the rising point of any body wanders east and west as you travel north or south. Near the poles the curve can double back or run almost flat across the map. It is common to see all four presented as if they were interchangeable objects. They are not, and a map that seems to behave strangely at high latitude is usually just the horizon geometry doing what it always does.
Because the Moon moves faster than any other body, its lines are also the ones most sensitive to birth time. An error of a few minutes shifts them noticeably.
What the tradition reads into lunar lines
The Moon carries habit, memory, food, family and the state a person falls back into when unobserved. On the IC line that symbolism is at its most concentrated: home, the family story, the place a person is said to feel unaccountably settled. The same accounts warn that it can pull a person backwards into old patterns, and both readings come from the same source.
The MC line puts private matters in public view. It is read as work that involves care, the public, food or the domestic, and as a place where moods are less easy to keep out of sight.
The AC line is read as heightened responsiveness, being easily affected by a place and its people. The DC line reads through others, often described as meeting people who feel immediately familiar, with the difficulty being an appetite for closeness that can outrun judgement.
These are readings, not forecasts. Nothing here says a place will do something to you.
Orb and the limits of the claim
The working orb quoted throughout the literature is roughly seven hundred to eight hundred kilometres either side, with the effect described as sharpest on the line and weakening as you move away. That range is convention. It was arrived at by practice and repetition rather than measurement, and you will find practitioners using tighter or looser figures without much dispute.
Keep the two halves of the technique separate. The geometry is computable to the kilometre, and any competent program will draw the same lines from the same birth data. What it means that a Moon IC line passes through a given city is interpretation supplied by a tradition, and it is fair to weigh it as such. Do not treat a map as a reason to move.
If you want the fuller picture, relocating the chart itself will show how the houses rearrange for a new city, which the lines alone do not tell you.
Questions people ask about this
What does a Moon line mean?
It marks where the Moon was angular at your birth. The tradition reads lunar lines through home, habit, care and emotional response, with the specific reading depending on which of the four angles is involved.
Why is my Moon AC line curved?
Rising and setting lines follow the horizon, whose tilt against the ecliptic changes with latitude. That produces a curve, and near the poles the curve can bend very sharply.
Does birth time matter for Moon lines?
More than for any other planet. The Moon moves about half a degree an hour, so even a few minutes of error shifts its lines. An unreliable birth time makes lunar astrocartography largely guesswork.
How wide is the orb on a Moon line?
About seven hundred to eight hundred kilometres is the usual figure, strongest on the line itself. It is a convention carried through the literature rather than a measured limit.
Who invented astrocartography?
Jim Lewis, in the 1970s. It is a modern technique that depends on computation, though the principle that angular planets are emphasised comes from much older material.
Is a Moon IC line a good place to live?
The tradition reads it as domestic and settling, and also as inward and backward looking. Neither is a promise, and no line is a sound basis for a decision about where to live.