Index value plots have a base index and graph a data set along that value, this is seen a lot when using a data set to figure out a trend line, such as a linear growth or decline, or a bell curve or sinosodal pattern in the data.
Found -http://www.scielo.br/img/revistas/jbchs/v15n2/19932f4.gif
This blog is a map catalog in which I am displaying fifty different types of maps and a tid-bit of information that looks into the purpose of the map!