Spatial Climate Analysis Service

Description of ARC/INFO ASCIIGRID File Format

ARC/INFO is a popular, commercial GIS package from ESRI Corp. ARC ASCIIGRID refers to a specifc ASCII format developed for ARC/INFO. ARC format consists of a header that specifies the geographic domain and resolution, followed by the actual grid cell values. ARC format grids are single-band files.

Records 1 - 6

Geographic header in ARC ASCIIGRID format:

ncols xxxxx	ncols refers to the number of columns in the grid and xxxxx is the numerical value
nrows xxxxx	nrows refers to the number of rows in the grid and xxxxx is the numerical value
xllcorner xxxxx	xllcorner refers to the western edge of the grid and xxxxx is the numerical value
yllcorner xxxxx	yllcorner refers to the southern edge of the grid and xxxxx is the numerical value
cellsize xxxxx	cellsize refers to the resolution of the grid and xxxxx is the numerical value
nodata_value xxxxx	nodata_value refers to the value that represents missing data and xxxxx is the numerical value.

Coordinates may be in decimal or integer format. DD:MM:SS format for geodetic coordinates is not supported.

Record 7 -> end of file

val(nox,noy) (f) = individual grid values, column varying fastest in integer format. Grid values are stored as integers but can be read as floating point values.

xllcorner and yllcorner are given as the EDGES of the grid, NOT the centers of the edge cells. ARC/INFO supports other header strings that allow the centers of the edge cells to be given, but they are not supported here. The origin of the grid is the upper left and terminus at the lower right.

The following is an example of the first few records in an ARC/INFO ASCIIGRID data file.

ncols 157
nrows 171
xllcorner -156.08749650000
yllcorner 18.870890200000
cellsize 0.00833300
0 0 1 1 1 2 3 3 5 6 8 9 12 14 18 21 25 30 35 41 47 53
59 66 73 79 86 92 97 102 106 109 112 113 113 113 111 109 106
103 98 94 89 83 78 72 67 61 56 51 46 41 37 32 29 25 22 19