In road districts so incorporated, each tract of land for forty acres, according to a government survey, and each of the smallest subdivisions of land that has been lawfully platted, and each separate tract of less than forty acres, shall, for the purpose of sections 233.320 to 233.445, be regarded as within one-half mile of any public road or part of public road, if the major portion thereof is within one-half mile; and over one-half mile and less than a mile if the major portion thereof is over one-half mile and less than one mile; and over one mile and less than one and one-half miles, if the major portion thereof is over one mile and less than one and one-half miles; and over one and one-half miles if the major portion thereof is over one and one-half miles.