0 a line drawn on a map that connects things with the same value, such as temperature or height above the earth's surface -- 等值线
When the number of variables is two, a level set is generically a curve, called a level curve, contour line, or isoline.
By generating classification results over the region of interest and using any contouring algorithm to separate the two classes, the isoline will have been retrieved.
A few types of maps that show the spatial layout of population are choropleth, isoline, and dot maps.
These included proportional point symbols, the line of equal value (isoline), the choropleth and shading, the dot method, class intervals, and flow lines.
Each isoline in a map of equivalent latitude follows that of an atmospheric tracer and encloses the same area as the latitude line of equivalent value, hence equivalent latitude.
