Bilateral Graph

http://www1.eere.energy.gov/vehiclesandfuels/facts/2008_fotw546.html
A bilateral graph is used to display two or more sets of related data on the same graph and can be a line graph, bar graph, or another type of graph. 

Nominal Area Choropleth Maps

http://politicalmaps.org/2008-house-of-representatives-election-maps/

A nominal area choropleth map is used to display nominal data which is simply data that can not be organized quantitatively. The data is grouped so that different colors represent different categories.  The map above displays the U.S. House Winners by district across the United States. 

Unstandardized Choropleth Maps

http://www.culturebore.com/2010/06/billion-dollar-language-barrier-in.html

An unstandardized choropleth map displays data sets as raw numbers instead of averaging the data.  The unstandardized choropleth map above shows which language is dominant in a particular area of Afghanistan.  

Standardized Choropleth Maps

http://mchb.hrsa.gov/mchirc/dataspeak/events/feb_08/materials/kirby_files/textonly/slide10.html
A standardized choropleth map uses standardized levels of data so that the data can be areally averaged and then compared to other areas of different sizes. The map above shows the standardized ratios of low birth weight.

Univariate Choropleth Maps

http://www.dailyyonder.com/files/images/

A univariate choropleth map simply displays a single variable across a region.  In this particular example above, we are viewing the percent of people living in poverty across the rural United States.  

Bivariate Choropleth Maps

http://www.personal.psu.edu/faculty/c/a/cab38/GEOG321/14_multivariate02/multivariate.html

A bivariate choropleth map is used to display two variables on a single map by combining two different sets of colors and is very useful in graphically illustrating the relationship between two spatially distributed variables.  The bivariate choropleth map above measure percent change and the population density across the United States. 

Unclassed Choropleth Maps

http://www.nws.noaa.gov/os/lightning/images/Vaisala_96-05_Flash_Map.gif
Unclassed choropleth map do not have an averaged statistic towards each particular color which means that the color shades are directly proportional to the values of each enumeration unit.  The unclassed choropleth map above shows the flash densities across the nation from 1996 to 2005.