ASC Arc/Info ASCII Grid File Description

Surfer imports and exports ASC Arc/Info ASCII grid files.

An Esri grid is a raster GIS file format developed by Esri. The ASCII format is also known as Arc/Info ASCII grid. The ASCII format is used as an exchange, or export format, with a simple ASCII file structure.

File Format

The first six lines of the file indicate the reference of the grid, followed by the values listed in the order they would appear (left to right and top to bottom).



ncols 4

nrows 6

xllcorner 0.0

yllcorner 0.0

cellsize 50.0

NODATA_value -9999

-9999 -9999 5 2

-9999 20 100 36

3 8 35 10

32 42 50 6

88 75 27 9

13 5 1 -9999


  • ncols is the numbers of rows (represented as integers)

  • nrows is the numbers of rows (represented as integers)

  • Lower-left corner refers to a cell corner, and not to a data point

  • xllcorner and yllcorner are the western (left) X coordinate and southern (bottom) Y coordinates, such as easting and northing (represented as real numbers with an optional decimal point)

  • xllcorner and yllcorner are the X and Y coordinates for the lower left corner of the lower left grid cell. Some ESRI raster files use xllcenter and yllcenter instead for the XY reference point, which indicate the X and Y coordinates for the center of the lower left grid cell. These values are represented as real numbers with an optional decimal point

  • cellsize is the length of one side of a square cell (a real number)

  • nodata_value is the value that is regarded as "missing" or "not applicable"; this line is optional, but highly recommended as some programs expect this line to be declared (a real number)

The remainder of the file lists the raster Z values for each cell, starting at the upper-left corner cell. The Z values are always reported for the center of each grid cell. These real numbers (with optional decimal point, if needed) and are delimited using a single space character.

File name extensions


Loading Files

Arc/Info ASCII grid files are similar to grid files and can be loaded to create a grid based map (i.e. Home | New Map | Contour), or when using the functions in the Grid menu.

Import Options Dialog

No import options dialog is displayed.

Import Automation Options

No import options are available.

Saving Files

Use the Grids | Edit | Convert command in the plot document, or File | Save As in the Grid Editor to export .AIG, .ASC, .AGR, and .GRD files. Alternatively, the ArcInfo ASCII Grid file format is available when prompted to save a grid file.

See Also

Open Grid

Export Options - Save Grid As

File Format Chart

Export Options - Spatial References