(a) Size and placement. No sign shall exceed 48 square feet in area. A permit for a 48 square foot sign is granted only when the sign is placed at least 10 feet back from the highway right-of-way. The part of the sign closest to the right-of-way is the point at which the measurement is taken. In general, the size of the sign is governed by its proximity to the highway right-of-way; i.e., the closer to the road the less area required to get the message across. All signs must be placed 10 feet from the highway right-of-way unless special circumstances require that they be placed closer. Special circumstances are: alignment of highway, terrain, existing trees or other natural features, or structure located on other parcels of real property, which might block or impair the view of the sign. Before a permit for a sign is granted, its location in relation to the blocking of visual access to existing signs is also considered. In circumstances in which a permit is granted for a sign closer than 10 feet to the right-of-way the square footage of the sign is reduced to the amounts stated in the following schedule: On edge of right-of-way--32 square feet
1 foot from right-of-way--33 square feet
2 feet from right-of-way--34 square feet
3 feet from right-of-way--35 square feet
4 feet from right-of-way--36 square feet
5 feet from right-of-way--37 square feet
6 feet from right-of-way--38 square feet
7 feet from right-of-way--39 square feet
8 feet from right-of-way--40 square feet
9 feet from right-of-way--41 square feet