The U.R. was created solely for application within the context of structure control.
The U.R. is not based on the sole consideration of surface area, it is directed more towards an economic approach. This also has an agricultural industry value (the U.R. varies according to the natural regions in the county).
The SMI is always used for social criteria: M.S.A., pension, etc
The U.R. is equal to around 2 SMI in most cases.
If the farm is located across several counties with different U.R. and S.M.I., the share of each is calculated (in proportion to the surface areas involved).