The generic data file for MISR is a swath, i.e., a set of measurements for the entire area observed during the day part of the orbit. This is a very large amount of data. To simplify the storing and processing of these data, swathes are broken into a series of predefined, uniformly-sized boxes along the ground track called blocks. Each path is divided into 180 blocks measuring 563.2 km (cross-track) x 140.8 km (along-track). For a given path, a numbered block always contains the same geographic locations. Hence, areas that are close to each other in latitude will belong to blocks with similar numbers. Because of seasonal variations in the portion of the Earth that is in daylight, only up to about 142 blocks will contain valid data at any particular time.