Levels Keyword
Used With Routines:  CONTOUR,  CONTOURFS,  CONTOUR2
Corresponding System Variable: None.
Specifies a vector containing the contour levels (maximum of 150) drawn by the CONTOUR and CONTOUR2 procedures.
A contour is drawn for each level specified in Levels. If omitted, the data range is divided into approximately six equally-spaced levels.
Example
To draw a contour plot with levels at 1, 100, 1000, and 10000:
CONTOUR, z, Levels=[1, 100, 1000, 10000]
To draw a contour plot with levels at 50, 60, ..., 90, 100:
c_levels = FINDGEN(6) * 10 + 50
CONTOUR, z, Levels=c_levels