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, access http://daac.ornl.gov/MODIS/modis.prj 

• For a prj.adf file, access http://daac.ornl.gov/MODIS/prj.adf 

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