To make up the lack of theoretical foundations for zoning, a notion of "balanced city" is proposed. A city is said to be balanced, if there exists a usage assignment between activity points such that for any pair of activity points linked in the assignment the distance between them does not exceed a certain permissible distance. This requirement, called an principle of balanced city, can be formulated into a mathematical program, which reduces to the balanced assignment program, one of integer programming problems. One proposition for the key step in its algorithm is stated.
