Whither urban industrial use?

   We are used to thinking of low-cost housing as the type of land use that suffers from zoning discrimination.  But in Washington, D.C., it's light industrial land use -- repair shops, cement plants, and recycling centers -- that is finding it harder and harder to operate under the city's zoning laws, according to a study.  Reasons include the development of land for non-industrial purposes, high land prices, and the fact that only five percent of the city is zoned for industrial.