The degree of cloudiness is indicated by how much of the circle is shaded

The coverage of clouds over a certain point is assessed to give a measure of current weather conditions. The sky is divided into quarters.

So if half the sky is covered with clouds, 'scattered clouds' are recorded and cover is reported as 2/4 or 1/2.  
 

Cloudiness	Description
0	No clouds
1/4	Isolated clouds
2/4	Scattered clouds
3/4	Broken clouds
4/4	Overcast

 
 
More information about clouds can be found in the Cloud atlas.

Weather symbol on maps

The degree of cloudiness is indicated by how much of the circle is shaded.