An astrological birth chart is a graphic representation of the skies at the time of a person or an event's birth. It is an actual map of the heavens relating the positions of the planets in the sky to the horizon and meridian of the earth. This is why it is essential that the place of birth and the time and date are provided with as much accuracy as possible because even small variations can produce important changes in the chart.
In this map of heavens it is possible to see, first of all, the Zodiacal Wheel that includes the 12 Zodiac signs. These are, in fact, the band of star constellations that we see in the sky and that have been named after animals or mythical characters after the observations of our ancestors.
Secondly, we can see the Sun, Moon and the eight other known planets* that are transiting through the Zodiac and station at a given sign at a person's birth time.
The astrological charts are also divided into 12 houses that function as an additional interpreting tool. The first house is started by the definition of the Ascendant (a zodiacal point that is found rising East in the sky at the time of the person's birth). From that point on and also based on the position of the meridian, the twelve houses are defined, including the other three angles in the chart (the Descendant, the Immum Coeli, known as the IC and the Midheaven, or MC), all with a particular significance in the astrological interpretation.
The birth-chart also symbolizes the map of the psyche of the individual, representing someone's potential development when he/she is born.
You can see an example of a Birth Chart by clicking here.
* Although Pluto has officially been disregarded as a planet by astronomers, its importance in Astrology is still the same.