Isolines Art Illustration: The
National Mall, the Washington Monument, Lincoln Memorial,
The National Mall is a national park in downtown Washington, D.C.,
the capital of the United States.
The term National Mall commonly includes areas that are officially part of West Potomac
Park and Constitution Gardens to the west, and often is taken to refer to the entire area
between the Lincoln Memorial and the United States Capitol, with the Washington Monument
providing a division slightly west of the center.
Source: Wikipedia, United States Capitol.
A contour line (also isoline, isopleth, or isarithm) of a function of two variables is a curve along which the function has a constant value.
Isolines usually have a parallel trend.