A Circle Graph, or that which is commonly termed as "Pie Chart," presents data through sectors illustrating frequency values.The arc length (or the total area) of each sector (or slice) is proportional to the value/quantity it represents. If all the sectors are combined, they create a full disk, resembling a pie.
Pie Chart beats Bar Chart in terms of popularity in the business world and mass media, since it is a more "artistic" way to present Graphical data.. The case for scientific and technical organizations is different; they rarely use Pie Charts. Statisticians recommend avoiding its use, saying that it is difficult to compare different sections of a given Pie Chart, or to compare data "across" different Pie Charts.
Pie Charts are particularly most effective to represent 25 to 50% of a data set. Bar Charts, Line Charts (dot plot), or tables are more advisable for large information representation.
There are many variants of Pie Charts; one of which is the Exploded Pie Chart. This Chart features one or more sectors separated from the rest of the disk. The effect is used to highlight a sector or highlight smaller segments of the disk with small proportions. Another is the Perspective (3D) Pie Chart. This type is more or less the same as the normal Pie Chart, and is often used only for aesthetic reasons. The 3D look in this variant does not improve the reading of the data at all.
The Polar Area diagram, developed by Florence Nightingale, is probably the most popular variant of Pie Chart. It is similar to the usual Pie Chart, except that the sectors differ not in the size of their "area" but in how far they extend from the center of the circle. This particular property makes it suitable for multiple comparisons on one diagram.