An astrology chart is a diagram showing where the planets are for a specific date, time and place. The chart is essentially a 2-dimensional map of the 3-dimensional sky – kind of like a photograph is a flat image of 3-dimensional objects.
Most charts display the positions of the planets relative to the horizon and the vertical longitude. Modern astrology charts are usually circular, whereas ancient astrology systems often used square charts.
There are different kinds of charts. When it is the chart of a person, it is called a Natal Chart or Birth Chart. A Horary chart is a divination technique for answering questions based on the chart of the moment.