The difference in cost between urban and rural telecommunications systems is predominately due to the distance from wire center to customers, and to the distances between customers. For any model to calculate rural customer costs accurately, it must accurately predict where rural customers are with respect to the wire center and to each other. In addition, since CBGs represent averaged information for large areas, they only vaguely define the customers distances from the wire center, and they do not define the distances between customers. While using CBs essentially solves the problem of defining distance from the wire center to the customer, it does not define the distance between rural customers. Rural America is very diverse.
Rural customers build their homes in every imaginable pattern.
The rural outside plant designer has to accept this, and the proxy models must represent this or universal support will be insufficient. Rural customers may cluster in groups of twos or threes, but this rural clustering is of little economic value to the modern loop designer who is trying to use electronic equipment based on 24 or 96 channel operation. The proxy models should not make unrealistic but economically convenient assumptions either. To estimate the cost of distribution and feeder outside plant to serve customers, it is necessary first to know where customers are located. The early versions of the cost models estimated customer location based on CBGs.