Polygraph
Topic: Graphical Representation of Data and Thematic Maps · NCERT: Class 12, Ch 3 "Graphical Representation of Data"
Meaning
A polygraph is a line graph with two or more lines. Each line shows a different variable or place. Each line gets its own style, such as solid, broken, dotted or dot-dash, or its own colour. This lets you compare several trends over the same period on one graph. For the exam, remember that NCERT describes a polygraph as showing "more than two variables". The statement "two variables only" is false.
Example
NCERT draws the sex ratio (number of females per 1,000 males) of Delhi, Haryana and Uttar Pradesh from 1961 to 2011 as three lines on one graph. Delhi's line rises from 785 in 1961 to 866 in 2011.
Don't confuse with
- Line graph: a line graph has one line for one variable. A polygraph puts several lines together so they can be compared.
- Multiple bar diagram: this also compares several variables, but it uses side-by-side bars instead of lines.