A different question from the rest of a chart
Everything else in astrology asks what you were born with. Astrocartography asks where on Earth each planet was doing something at that moment: rising, setting, directly overhead, or directly underfoot.
The chart itself does not change. The planets stay exactly where they were; what changes as you move across the map is the horizon and the meridian they are measured against, and therefore which houses they occupy.
The four line types
Each body gets a line for each of the four angles. The calculator draws every one of them and lets you filter down to what you want to look at.
| Line | Where the planet was | Conventionally read for |
|---|---|---|
| MC | Directly overhead | Career, standing, what you are known for there |
| IC | Directly underfoot | Home, roots, private life |
| ASC | Rising in the east | How you come across, what you become there |
| DSC | Setting in the west | Partnership, who you attract there |
Midheaven and Imum Coeli lines are meridians: single longitudes running pole to pole, drawn straight on the map. Ascendant and descendant lines are curves, because whether a body is on the horizon depends on latitude as well as longitude.
Reading the map without overreading it
A line marks where an influence is strongest, and the conventional orb is a few hundred miles either side. Beyond that the effect is generally considered to fade rather than stop abruptly, and different practitioners use different distances.
The honest framing is that this technique describes emphasis rather than outcome. A Venus line does not make a city pleasant; it describes which part of your own chart gets amplified while you are there. People who have lived on several lines usually report the amplification and rarely report the specific promises found in popular writing.
Nothing about the method predicts events, and no line is a reason to move somewhere. It is a lens rather than an instruction.
Which lines are worth attention
Start with the fast bodies and the angles. Sun, Moon, Venus, Mars and Jupiter lines are the ones people report most consistently, and the Midheaven and ascendant lines of any body are stronger than its IC and descendant lines in most accounts.
Saturn lines have the worst reputation and the most interesting reports. People describe them as demanding rather than unlucky, and a Saturn Midheaven line is a common feature in the biographies of people who built something serious somewhere difficult.
Outer planet lines cover enormous stretches of the map for an entire generation, which limits how personal they can be. Use the filters to take them out when the map gets crowded.
Why this needs an exact birth time
Every line here is measured from the horizon or the meridian, and both sweep the entire globe once a day. A birth time an hour out moves every line about fifteen degrees of longitude, which is roughly a thousand miles at mid-latitudes.
That is a bigger error than the technique can absorb. The calculator refuses to draw the map without a time rather than producing something that looks precise and is not.
Relocation charts, and how they differ
Astrocartography draws lines on a map. A relocation chart recalculates the whole chart for one specific place, giving you the actual house cusps you would be living under there.
The two answer different questions. Use the map to find candidates and the relocation chart to examine one properly, since the map only shows the four angular contacts while the relocated chart shows every placement's new house.
What the map projection means for accuracy
The map here is equirectangular, which is the standard for this technique: longitude and latitude map to a simple grid. It distorts area badly at high latitudes, so a line that looks like it covers half of northern Canada covers less ground than it appears to.
The Midheaven longitudes are listed as numbers underneath the map for that reason. A longitude is unambiguous in a way a drawn line on a projection is not, and it is what to use if you want to check a specific city.
Common questions
What do the lines actually mark?
Where each planet was rising, setting, directly overhead or directly underfoot at the moment you were born. The chart does not change as you move; the horizon it is measured against does.
How wide is a line?
Conventionally a few hundred miles either side, fading rather than stopping. Practitioners use different distances, which is worth knowing before treating any boundary as precise.
Why do I need an exact birth time?
Every line is measured from the horizon or meridian, and both sweep the globe once a day. An hour of error moves every line about fifteen degrees of longitude, roughly a thousand miles at mid-latitudes.
Should I move to a good line?
Nothing here predicts events, and no line is a reason to relocate. The technique describes which part of your own chart gets amplified somewhere, which is a lens rather than an instruction.
Which lines matter most?
The fast bodies and the angular contacts. Sun, Moon, Venus, Mars and Jupiter lines are reported most consistently, and Midheaven and ascendant lines more than their opposites.
What is the difference from a relocation chart?
The map shows only the four angular contacts. A relocation chart recalculates every house cusp for one specific place, so use the map to find candidates and the relocation chart to examine one.