Where the lines come from
An astrocartography map is a birth chart redrawn across the globe. The moment of birth is held fixed and the question is asked of every location: from here, was Mars rising, setting, culminating, or at the lowest point? Each of those four conditions traces a line, and the four together are the planet's contribution to the map.
Jim Lewis developed this in the 1970s. It is a modern technique, dependent on computing power that older astrologers did not have. The traditional idea it draws on is angularity, the rule that a planet on one of the chart's four angles is emphasised more than one placed elsewhere.
Two meridians and two curves
The Mars MC line runs through the longitudes where Mars was culminating, on the meridian overhead. The Mars IC line marks where it sat at the lowest point, on the meridian below. Both are straight north to south lines, because a meridian is a fixed circle through the poles and is the same at every latitude.
The AC line, where Mars was rising on the eastern horizon, and the DC line, where it was setting in the west, curve instead. The horizon's tilt against the ecliptic varies with latitude, so the rising point shifts as you travel toward or away from the equator. The result is a curve that can bend sharply, and at extreme latitudes behave in ways that look like errors and are not. Most write-ups treat all four lines as the same kind of object, which is why the maps then seem inconsistent.
What Mars lines are read for
Mars signifies effort, conflict, appetite, cutting, competition and heat. The tradition is unusually candid about the difficulty here. The MC line is read as ambition made visible, work with a competitive edge to it, and also as friction with people in authority and a reputation for being combative.
The IC line is read as energy turned inward on the home, restlessness, arguments in the household, and hard physical work done privately. The AC line is described as a place where a person is met as forceful and acts quickly, with irritability and accidents as the standard warnings. The DC line reads through others, associated with strong partnerships and with open conflict, depending on which account you read.
All of that is interpretation. It describes what the symbolism has been taken to indicate, not something a place will do to a person. Plenty of people live on Mars lines with no story to tell about it, and no map should be treated as a warning to stay away.
Orb, and how much weight the method bears
The orb given for a line is a few hundred kilometres, most often stated as seven hundred to eight hundred, with the reading strongest exactly on the line and weaker as you move off it. That number circulates because it is convenient and repeated, not because a study established it. Different practitioners use different figures, which is itself informative.
Here is the honest framing. Astrocartography is geometry applied to a symbolic system. The geometry is exact and computable, which is why lines can be drawn to the kilometre and why any two programs will agree given the same birth data. What a Mars line means where it crosses a city is convention, added by a tradition of readers. Do not take a line as a reason to move somewhere, and do not take one as a reason to avoid a place either.
If you want more than the lines, a relocated chart will show the houses redrawn for a specific city, and parans mark latitudes where Mars is angular alongside another planet.
Questions people ask about this
Are Mars lines bad?
The tradition reads them as difficult, with conflict, haste and irritability named directly. That is a description of the symbolism, not a verdict on a place, and this page does not treat any line as good or bad fortune.
What does the Mars MC line mean?
It marks longitudes where Mars was culminating. The reading is public ambition and competitive work, along with friction with authority and a reputation for pushing hard.
Why is the Mars AC line curved on the map?
Rising lines follow the horizon, and the horizon meets the ecliptic at an angle that changes with latitude. That produces a curve rather than a straight meridian, and the bend grows severe at high latitudes.
How wide is the influence of a Mars line?
Conventionally about seven hundred to eight hundred kilometres, strongest on the line. The figure is a habit of the literature rather than a measured range, and practitioners differ.
Who created astrocartography?
Jim Lewis, working in the 1970s. It is a modern method built on the older astrological principle that angular planets carry more weight.
Should I avoid cities on my Mars line?
There is no basis for advising that. The geometry is exact but the meaning is convention, and a decision about where to live should rest on things that can be checked.