Scale models of people and animals are found in a wide variety of venues, and may be either single-piece objects or kits that must be assembled, usually depending on the purpose of the model. For instance, models of people as well as both domestic and wild animals are often produced for display in model cities or railroads to provide a measure of detail or realism, and scaled relative to the trains, buildings, and other accessories of a certain line of models. If a line of trains or buildings does not feature models of living creatures, those who build the models often buy these items separately from another line so they can feature people or animals. In other cases, scale model lines feature living creatures exclusively, often focusing on educational interests.