c = velocity  l = wavelength = vector between crests  w = time frequency 
In this picture, the level lines are the sloped lines on the right. On the left, these are the level lines if Ax = constant. The equation of the level lines on the right is y = (A/B)x + constant. 
Ax + By = 0 [A,B] * [x,y] = 0 [A,B] __ [x,y] 
The "curve" Ax + By = 0 is the line through the origin __ [A,B] 
In this example each line is separated by 1. 
c / sqrt(A² + B²) 
from the line Ax + By = 0, c > 0 if the line is in the direction of [A,B]. 
y = A * cos(ax + by + cz)  l = wavelength vector, perpendicular to the level lines.  
l = a multiple of [a,b,c], the signed distance from level 0 to level 2p is equal to:

