Subdivision ordinances frequently mandate regarding to bring the actual land closer to the billiard-table ideal and that, in turn, requires stripping all existing vegetation. To preserve the ecosystem, a different approach is needed. A generation ago Ian McHarg in Design with Nature outlined a method of classifying land according to its carrying capacity for new development. Land judged to be the least subject to environmental constraints would be the best place to build. Lane Kendig in his book, Performance Zoning, shows how to take the kind of environmental analysis McHarg advocates and apply it to zoning.
Most zoning codes relate development density to land area.
Kendig outlines a system of discounting land areas based on the sensitivity of the land to disturbance during development. For example, a portion of the site that is actually under water would be discounted 100 percent, shoreline areas 75 percent, mature woodlands 85 percent, slopes of 15 degrees or greater 70 percent, and so on. Making these discounts an amendment to a zoning text can reduce development density in environmentally sensitive areas without controversial changes to the current zoning map or community-financed site surveys that determine precisely where the sensitive areas are located. A developer applying for a building permit must present, as part of the application, a site map showing all natural features, with contours described at two-foot intervals. Areas of environmental sensitivity are computed, discounted, and the zoning densities adjusted accordingly.