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Esri ASCII raster format

  • Header format
  • Data format
  • Example ASCII raster:

The Esri ASCII raster format can be used to transfer information to or from other cell-based or raster systems. When an existing raster is output to an Esri ASCII-format raster, the file will begin with header information that defines the properties of the raster such as the cell size, the number of rows and columns, and the coordinates of the origin of the raster. The header information is followed by cell value information specified in space-delimited row-major order, with each row separated by a carriage return.

To convert an ASCII file to a raster, the data must be in this same format. The parameters in the header part of the file must match correctly with the structure of the data values.

The basic structure of the Esri ASCII raster has the header information at the beginning of the file followed by the cell value data:

The basic structure of the Esri ASCII raster has the header information at the beginning of the file followed by the cell value data. The spatial location of the raster is specified by the location of the lower left cell, and either by:

  • The center of the lower left cell

    NCOLS xxx
    NROWS xxx
    XLLCENTER xxx
    YLLCENTER xxx
    CELLSIZE xxx
    NODATA_VALUE xxx
    row 1
    row 2
    ...
    row n

  • The lower left corner of the lower left cell

    NCOLS xxx
    NROWS xxx
    XLLCORNER xxx
    YLLCORNER xxx
    CELLSIZE xxx
    NODATA_VALUE xxx
    row 1
    row 2
    ...
    row n

Row 1 of the data is at the top of the raster, row 2 is just under row 1, and so on.

Header format

The syntax of the header information is a keyword paired with the value of that keyword. These are the definitions of the keywords:

ParameterDescriptionRequirements

NCOLS

Number of cell columns

Integer greater than 0.

NROWS

Number of cell rows

Integer greater than 0.

XLLCENTER or XLLCORNER

X-coordinate of the origin (by center or lower left corner of the cell)

Match with y-coordinate type.

YLLCENTER or YLLCORNER

Y-coordinate of the origin (by center or lower left corner of the cell)

Match with x-coordinate type.

CELLSIZE

Cell size

Greater than 0.

NODATA_VALUE

The input values to be NoData in the output raster

Optional. Default is -9999.

ASCII header information

Data format

The data component of the Esri ASCII raster follows the header information.

  • Cell values should be delimited by spaces.
  • No carriage returns are necessary at the end of each row in the raster. The number of columns in the header determines when a new row begins.
  • Row 1 of the data is at the top of the raster, row 2 is just under row 1, and so on.

Example ASCII raster:

ncols 480
nrows 450
xllcorner 378923
yllcorner 4072345
cellsize 30
nodata_value -32768
43 2 45 7 3 56 2 5 23 65 34 6 32 54 57 34 2 2 54 6 
35 45 65 34 2 6 78 4 2 6 89 3 2 7 45 23 5 8 4 1 62 ...

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