![]() ![]() The spatial data for a grid is automatically split across multiple tiles if the size of the grid at the time of creation is larger than the upper limit for the size of a tile. As a result, most grids used for GIS applications are automatically stored in a single tile. The upper limit on the size of a tile is set by the application and is very large (currently set at 4,000,000 x 4,000,000 cells). The size of the tile for a grid is based on the number of rows and columns in the grid at the time of creation. Each block is stored as one variable-length record. Blocks are stored on disk in compressed form in a variable-length file structure referred to as a tile. Grids are implemented using a tiled raster data structure in which the basic unit of data storage is a rectangular block of cells. A multiple-band grid cannot have more than 9 characters in its file name, and a single-band raster dataset cannot have more than 13 characters. Caution:Īs with most formats, a grid should not be named with spaces or any other special characters in its name. Grids also carry additional information, such as the coordinate system associated with the grid. The coordinate system of a grid is thus defined by the cell size, the number of rows and columns, and the x,y coordinate of the upper left corner. Since each cell within a grid has the same dimension as other cells, the location and area covered by any cell is easily determined by its row and column. The rows and columns are parallel to the x- and y-axes of the coordinate system. The coordinate system of a grid is the same as that of other geographic data. An integer grid may have other INFO items added to its VAT whose range of values depends on the item definition.
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