The importance of maintaining up-to-date information about the often changing environment around airports (e.g., vertical obstructions to air traffic, such as cranes, can be erected at short notice), ILS charts are published with expiration dates and are reviewed on a frequent basis. Since ILS Charts often contain extra information relative to the procedure they depict, some of the updates are done purely because of the changing environment around airports, in which case none of the procedural elements are changed. Anytime the procedure is changed, the plate is re-issued with the updated information. All the ILS charts are georeferenced with all the required definations. Sample ILS chart as follows