A quadrat is a  square (of either metal, wood, or plastic) used in ecology and geography to isolate a sample, usually about 1m² or 0.25m². The quadrat is suitable for sampling plants, slow-moving animals (such as millipedes and insects), and some aquatic organisms. When an ecologist wants to know how many organisms there are in a particular habitat, it would not be feasible to count them all. Instead, he or she would be forced to count a smaller representative part of the population, called a sample. Sampling of plants or animals that do not move much (such as snails), can be done using a sampling square called a quadrat. A suitable size of a quadrat depends on the size of the organisms being sampled. For example, to count plants growing on a school field, one could use a quadrat with sides 0.5 or 1 meter in length.