misperceptions. For example, due to the simultaneous contrast effect, the Bezold effect, and other factors, an area shaded light red surrounded by areas shaded dark red will appear even lighter. Differing shades of red and blue compound this effect. Cartographers have traditionally limited the number of classes so that it is always obvious which class a color shade represents. Some election maps, however, have violated this tradition by simply coloring each areal unit with a red-blue mixture linked to voting ratio data—resulting in an "unclassified choropleth map". These "purple maps" are useful for showing the highly mixed nature of voting, but are extremely difficult to interpret in detail. The lack of clear classes make these purple maps prone to the problems of color perception described above. However, there are pros and cons to both classified and unclassified choropleth maps. Each tend to show some patterns well while obscuring others. All these facts should be taken into account when looking at election maps. Critiques The paradigm has been criticised on several fronts. Many argue that assigning partisanship to states is only really useful as it pertains to the Electoral College, as well as (more recently) the Senate, primarily a winner-take-all system of elections (with the exceptions of Nebraska and Maine). The Democratic or Republican party of a particular state may have policies that depart—sometimes greatly—from those of the national party, sometimes causing that state to favor one party in state and local elections and the other in presidential elections. This is most evident in the Southern United States, where the state Democratic Party organizations tend to be more conservative than the national party, especially on social issues. Likewise, Republicans have elected many statewide officeholders in states that are very Democratic for presidential elections, such as Massachusetts, Illinois, Maryland, Vermont, and New Jersey. The elections in Arkansas as well as West Virginia in 2004 were won by Republican President George W. Bush, but Democrats at the time held all four U.S. Senate seats and majorities of elected executive officeholders in those states, including the governorship of the latter. Similarly, Tennessee was won by Bush in both 2000 and 2004, but going into 2004, its governor was a Democrat and both chambers of the state legislature were controlled by Democrats as well. The converse can also be true, as in the case of Maine, which had two Republican U.S. senators, but Democratic presidential