THAT WHICH IS CLAIMED: 1. A method comprising: receiving a picture; encoding the picture as one or more slices; encoding, into a slice header of a slice of the one or more slices, one or more tile identifiers indicative of one or more tile positions for one or more tiles in the slice; and encoding one or more assignments of one or more tile identifier values for the one or more tile identifiers indicative of tile positions in a parameter set file. 2. A method according to Claim 1 further comprising: encoding, into the slice header, a block index relative to a tile of the one or more tiles, wherein the block index comprises a syntax element indicative of a block position for a block within the tile. 3. A method according to any of Claims 1 to 2 wherein one tile identifier of the one or more tile identifiers is indicative of a tile that comprises a pre-defined block of the slice. 4. A method according to any of Claims 1 to 3, further comprising: constructing one or more motion vectors associated with one or more prediction units in one or more coding units in the one or more tiles, wherein the one or more motion vectors apply in one or more anchor locations derived from one or more anchor location identifiers defining a position relative to the one or more tiles indicated by the one or more tile identifiers. 5. A method according to any of Claims 1 to 4, further comprising: constructing a decoding order constraint file associated with the picture, wherein the decoding order constraint file includes a reorder indication indicating whether the one or more tiles are able to be reordered without affecting decodability for the one or more tiles. 6. An apparatus comprising at least one processor and at least one memory including computer program code for one or more programs, the at least one memory and the