Discover Your
Astrocartography Map

What the calculator draws

An astrocartography map projects one moment, the moment of birth, onto the whole globe. At that instant every planet stood on the eastern horizon somewhere, on the western horizon somewhere else, on the upper meridian along one line of longitude and on the lower meridian along the opposite one. Join up those places for the ten planets and you have 40 lines. Jim Lewis made the technique popular under the name Astro*Carto*Graphy, mailing hand-drawn maps to clients from 1976.

Once a map is drawn, this calculator gives you:

• The 40 lines, each labeled at the map's top and bottom edges with the planet's glyph and the angle: MC solid, IC long dashes, ASC solid, DSC short dashes.
• A hover box (on a desktop) with the coordinates under the cursor, the Ascendant and Midheaven of a chart cast for that point, and the nearest line with its distance in kilometers.
• A city search that pins a place and lists up to five lines within 1,500 km of it, nearest first.
• Crossings and parans: the points where two lines meet, and the band of latitude through each one.
• Filters for planets and angles, and four presets: Career (Sun, Jupiter and Saturn MC), Love (Venus and Moon DSC), Home (Moon and Venus IC) and Growth (Sun and Jupiter ASC).
• A card with the three lines nearest the birthplace, an interpretation for every line, a PNG download and a link that reopens the same map.

The map depends on the moment only, in universal time. The birthplace matters for converting the local clock time and for the distances, but two people born at the same instant in different cities have identical maps.

How the lines are calculated

Planet positions come from the site's ephemeris. For each planet the server takes the point of the ecliptic at the planet's longitude and converts it to right ascension and declination using the true obliquity of the date. That point is on the Midheaven wherever the local sidereal time equals its right ascension, on the IC 180° later, and on the Ascendant or Descendant when its hour angle equals its semi-diurnal arc, the half-day arc fixed by latitude and declination (cos H₀ = −tan φ · tan δ). Subtracting the Greenwich sidereal time at birth turns each of those sidereal times into a longitude, row by row every 0.5° of latitude from 66°S to 66°N. These are exactly the places where a standard house calculation, run for each spot, puts the Ascendant or Midheaven on the planet's degree (the Descendant and IC lines are where it puts them on the opposite degree). Checked against that calculation, all 10,600 points of Prince William's map agree within 0.39′.

The Midheaven depends only on the sidereal time, not on latitude, so MC and IC lines are meridians running due north and south, and a planet's IC line lies exactly 180° of longitude from its MC line. The Ascendant depends on latitude as well, so ASC and DSC lines curve, most for planets whose zodiac degree has a large declination, such as the Sun near the solstices. The lines stop at 66°, just short of the polar circles (66°33′ for a 1982 birth), beyond which some degrees of the zodiac stop rising and setting.

Every crossing joins one planet's ASC or DSC line to another's MC or IC line: two meridian lines are parallel, and two curved lines cannot meet because a place has only one Ascendant. The server solves each crossing's latitude exactly from the same formulas. Parans are the crossings grouped into 1° bands of latitude, each crossing assigned to the nearest whole degree. Before anything is drawn, the browser checks every point and crossing against the Ascendant and Midheaven computed for that spot and drops any that disagree. On Prince William's map nothing fails the check.

Zodiacal lines, not in mundo

There are two ways to say where a planet is on an angle. The zodiacal method used here puts the planet's degree of the zodiac on the angle and ignores its latitude, its distance north or south of the ecliptic. The in mundo method uses the planet's true position and marks where the body itself rises, sets or crosses the meridian. The documentation of Walter Pullen's Astrolog program describes in mundo as the form Jim Lewis popularized. Zodiacal lines have one practical advantage: they agree with a relocated chart. On a zodiacal ASC line, a chart cast for that place has the planet exactly on the Ascendant degree.

The difference grows with a planet's latitude. The Sun has none, so its lines are the same either way. On Prince William's map the Moon, 0°46′ south of the ecliptic, would have its in mundo ASC line 91 km from the zodiacal one at London's latitude. Pluto, 17°17′ north of the ecliptic, is the extreme case: its in mundo MC line runs 6°19′ of longitude east of the zodiacal one, and its ASC lines are 981 km apart on London's parallel.

In mundo positions from the same ephemeris (right ascension and declination, no refraction), computed for comparison only; the map draws zodiacal lines.

How far a birth-time error moves the lines

The Earth turns one degree in a little under four minutes, so an error in the birth time slides the whole map east or west: a later time moves every line west, an earlier one east. The MC and IC lines move exactly as far as the curved ones. A common claim that meridian lines are safer with an uncertain time is wrong; they keep their shape, not their place.

Redrawing William's map for 21:18, 15 minutes after the recorded time, moves every line about 3°44′ west. The Moon's lines move a little less, 3°35′, because the Moon itself advanced 0°09′ through the zodiac in that quarter hour. In distance the shift depends on latitude:

So the useful precision of a map is the precision of the birth time. With a time rounded to the nearest half hour, a city 260 km from a line at London's latitude may in fact sit on it, or twice as far away.

Reading the map

1. Start with the places that matter to you: where you live, work, grew up or are thinking of moving. Pin each one with the city search and note the lines it lists.
2. For each line, read the angle before the planet. The MC concerns work and standing, the IC home and family, the ASC yourself and your body, the DSC partners and the people you deal with.
3. Then read the planet in that role, using its page in the guide below. A planet that works well in your birth chart is usually read more kindly on a line than one under strain.
4. Check the crossings and parans near your places. Turn parans on in the filters to see their latitude bands drawn across the map.
5. Hover over a city to see the Ascendant and Midheaven there: the relocated chart is the same reading as the lines, seen from one spot.
6. Weigh every distance against the accuracy of the birth time, as the table above shows.

The step-by-step guide, with a worked example for each stage, is how to read your astrocartography map. For particular goals, see the lines astrologers read for love, career, money and health.

Worked example: Prince William's map

The birth was at 9:03 PM on June 21, 1982, in Paddington, London, as the official announcement gave it (20:03 UT). Three lines pass within 157 km of the hospital: the Neptune ASC line at 116 km, the Jupiter MC line at 130 km and the Sun DSC line at 157 km. A chart cast for central London has 27°31′ Sagittarius rising and 2°30′ Scorpio on the Midheaven, and those are the figures the hover box shows there.

The whole map has 74 crossings in 46 paran bands. London falls in the 52°00′N band, which holds two crossings: Mercury DSC / Mars MC and Jupiter MC / Neptune ASC. The Jupiter MC line runs down 2°03′W, and the paran through its crossing with Neptune's ASC line runs across England. Open William's map to check each figure, or enter your own birth data above.

What each planetary line means

Each planet has a page on its four lines, with where they ran on a real chart. Start with the planets on the lines nearest your places.

Frequently Asked Questions