ESRI ASCII Raster format

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 seperated by a carraige return.

In order 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:

    NCOLS xxx

NROWS xxx

XLLCENTER xxx | XLLCORNER xxx

YLLCENTER 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. The definitions of the kewords are:


Parameter Description Requirements
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.

Data format

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

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 ...