Contours
A set of lines drawn to represent the configuration of a 2d or 3D
surface. Each line is a constant value of a given quantity, drawn
among a series of points on the surface.
The generic name for contour lines is isopleths
Rules and strategy
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Choose a contour interval which shows the necessary structure without being cluttered
Find local maximums and minimums first. Start drawing around one of these.
Perform quality control to remove obviously bad data
Draw light and sketch with a pencil. It is common to erase and adjust the lines while sketching.
Interpolate between given values to correctly place an isopleth
Final lines should be smooth
Label your lines on each end, and in the middle if it’s a long line.
Put an "H" or "L" at places where values are higher or lower than their surroundings--that is, at
local maxima and minima. This is usually reserved for pressure fields but sometimes done for other
fields.
• Contour lines never cross each other.
• Contour lines never branch or fork.
• Never extrapolate where no data exists
Characteristics
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Widely spaced contours indicates flat surface (weak gradient)
Closely spaced contours indicates steep surface (tight gradient)
Equally spaced contours indicates uniform slope of the surface
Approximately concentric closed contours with decreasing values towards center indicate a local
minimum
• Approximately concentric closed contours with increasing values towards center indicate a local
maximum
• Contour lines which curve at a local minimum indicate a trough
• Contour lines which curve at a local maximum indicate a ridge
Common isopleths
Iso --- contour of constant value; isallo --- contour of value change
Isobar
Pressure
Isotherm
Temperature
Isotach
Wind speed
Isogon
Wind direction
Isodrosotherm
Dewpoint
Isohyet
Precipitation accumulation
Isallobar
Pressure change
Isohypse
Geopotential height
Isohume
Humidity
Isohaline
Salinity
Isopycnic
Density
Isoneph
Cloudiness
Isohel
Sunshine
Isoshear
Windshear
Isodop
Doppler velocity values
Isentropes
Potential temperature
Example