ASCII Grid Format Description

Overview

ASCII Grid format is a good means of distributing raster image data files: it is an ASCII format so it is both human readable and hardware independent; it is widely supported and easy to import and export from most GIS software, easy to convert with a small script if necessary, and stores data in a reasonably compact raster format when compressed.

Format

• The ASCII file must consist of header information containing a set of keywords, followed by cell values in row-major order.
• Cell values should be delimited by spaces. No carriage returns are necessary at the end of each row in the grid.
• The number of columns (NCOLS) in the header is used to determine when a new row of data values begins.
• The number of data values (cell values) must be equal to the number of rows (NROWS) times the number of columns (NCOLS).
• Row 1 of the data is at the top of the grid, row 2 is just under row 1, and so on.
• The keyword NODATA_VALUE is optional and defaults to -9999.
• The NODATA_VALUE is to be assigned to those cells whose true value is unknown. In the imported grid they will be assigned the keyword NODATA.
• The file format is:xxx (Where xxx is a number.)

<NCOLS xxx>

<NROWS xxx>

<XLLCENTER xxx | XLLCORNER xxx>

<YLLCENTER xxx | YLLCORNER xxx>

<CELLSIZE xxx>

{NODATA_VALUE xxx}

row 1

row 2

.

.

.

row n

Resources

Links to projection (sinusoidal coordinate system) files for the MODIS Land Product ASCII GRID formatted data:

• For a PRJ file, click here
• For a prj.adf file, click here

For assistance with importing ASCII Grid format data files into common GIS packages, please refer to ASCII_Grid_GIS_Help.pdf.

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