elements. When the term "tile grid" is referred in various embodiments, those embodiments can similarly be realized with the grid specified by these syntax elements or alike, hereafter referred to as the identifier grid. The semantics of slice tile id may be specified to be the first coding tree block in the slice segment is the top-left coding tree block of the grid cell (of the identifier grid) that is identified by the slice tile id value. [00137] In an embodiment, the vertices of the tile grid collocate with the vertices identifier grid but may be sparser. The vertices of the tile grid may be indicated relative to the identifier grid, i.e., it may be indicated which vertex of the identifier grid is also a vertex of the tile grid. For example, the following syntax may be used: [00138] tile_column_flag[i] specifies whether the i-th (right-side) column boundary in the identifier grid is a tile column boundary. If tile_column_flag[i] is equal to 1, the i-th (right- side) column boundary in the identifier grid is a tile column boundary. If tile_row_flag[i] is equal to 0, the i-th row boundary (below the i-th row) in the identifier grid is not a tile row boundary. tile_column_flag[i] specifies whether that the i-th row boundary in the identifier grid is a tile row boundary. If tile_column_flag[i] is equal to 1, the i-th row boundary in the identifier grid is a tile row boundary. [00139] The use of the identifier grid facilitates mixed use of motion-constrained slices and MCTSs in some use cases. [00140] In some embodiments tile identifiers are assigned to tile positions in a raster scan order of tiles within a tile grid. In some embodiments, the tile identifiers take the form of tile id syntax elements or alike. The tile id values may be assigned in a pre-defined manner, e.g., 0, 1, 2, 3, ... in raster scan order of tiles within the tile grid. [00141] In an embodiment, tile identifier values (i.e., tile id values or alike) are explicitly assigned to tile positions in or along the bitstream, e.g., in a picture parameter set, e.g., as a list of tile identifier values in in raster scan order of tiles within the tile grid. In the absence of indicated identifiers, a pre-defined indexing scheme may be utilized.