A method of decoding a stream of encoded data the method comprising, at a decoder: receiving an encoded dataset comprising multiple tiles; receiving a data structure, said data structure indicative of the amount of data required to encode a plurality of tiles; identifying a portion of the encoded dataset to be decoded by: identifying the tiles associated with the portion to be decoded; determining the location of data related to the tiles based on the amount of data required to encode said tiles; extracting the identified portion of the encoded dataset from the encoded dataset; and decoding said identified portion of the encoded data set.