A bird atlas is an ornithological work that attempts to provide information on the distribution, abundance, long-term change as well as seasonal patterns of bird occurrence and make extensive use of maps. They often involve a large numbers of volunteers to cover a wide geographic area and the methods used are standardized so that the studies can be continued in the future and the results remain comparable. In some cases the species covered may be restricted to those that breed or are resident. Migration atlases on the other hand cover migratory birds depict maps showing summaries of ringing and recoveries.