A birth chart, also called a natal chart, is a structured view of calculated celestial positions and chart angles for a stated birth time and place. It usually shows zodiac positions, houses, and aspects according to declared conventions.
The positions and angles are calculation results. The meanings assigned to them belong to astrological traditions and are not scientifically validated personality measurements or event predictions.
A reproducible chart names its timestamp and timezone treatment, coordinates, zodiac, house system, software or method, and relevant tolerances. When birth time is unknown, time-sensitive results such as the Ascendant and houses should be omitted or marked uncertain rather than guessed.
Birth details are personal data. A privacy-preserving calculator can perform the calculation in the browser without transmitting or storing the inputs. The birth-chart guide gives a five-pass reading order; the Big Three guide explains the first three placements.
Sources and further reading
The project methodology records calculation settings and provenance; the privacy boundary records how calculator inputs are handled. Neither page presents chart interpretation as a scientific personality test.