What is field category?
The field category is one of the parameters that influence the actions of the wind.
It is a characteristic of the surface condition of the terrain that depends on the obstacles present on the ground with their various heights and density.
Thus, the presence of obstacles such as buildings or vegetation will disturb the flow and lead to low wind speeds.
Conversely, in open areas (e.g. seashore), nothing will slow the wind and its speed will be higher. Similarly, a tall building will be less sensitive to the effect of obstacles on the ground.
This is translated in EN 1991-1-4 by the roughness coefficient cr(z).