Esri grid

An ESRI grid is a raster GIS file formats developed by ESRI, which has two formats:

1. A proprietary binary format, also known as an ARC/INFO GRID, ARC GRID and many other variations
2. A non-proprietary ASCII format, also known as an ARC/INFO ASCII GRID

The formats were introduced for ARC/INFO. The binary format is widely used within ESRI programs, such as ArcGIS, while the ASCII format is used as an exchange, or export format, due to the simple and portable ASCII file structure.

GIS grid

The grid defines geographic space as an array of equally sized square grid points arranged in rows and columns. Each grid point stores a numeric value that represents a geographic attribute (such as elevation or surface slope) for that unit of space. Each grid cell is referenced by its x,y coordinate location.

File formats

ASCII

The format is relatively straight-forward: the first six lines indicate the reference of the grid, followed by the values listed in the order they would naturally appear (left-right, top-down). For example, consider a grid, shown to the right. This could be encoded into an ASCII grid file, that would look like:

Grid layout	ASCII grid
1 2 3 4 1 5.5 −12.3 12.0 −8.5 2 NA −6.2 −8.1 −5.3 3 −9.4 0.0 −6.1 NA 4 −7.7 −6.4 3.6 10.7 5 −8.1 −13.2 −11.1 −2.6 6 NA NA 16.6 19.5	ncols 4 nrows 6 xllcorner 0.0 yllcorner 0.0 cellsize 100 nodata_value -9999.0 5.5 -12.3 12.0 -8.5 -9999.0 -6.2 -8.1 -5.3 -9.4 0.0 -6.1 -9999.0 -7.7 -6.4 3.6 10.7 -8.1 -13.2 -11.1 -2.6 -9999.0 -9999.0 16.6 19.5

where

ncols is the number of rows (an integer);

nrows is the number of columns (an integer);

xllcorner is the western (left) x-coordinate (such as Easting);

yllcorner is the southern (bottom) y-coordinate (such as Northing);

cellsize is the length of one side of a square cell; and,

nodata_value is the value that is regarded as "missing" or "not applicable"; this line is optional.

The remainder of the file, from line 7 onwards, lists the raster values for each cell, starting at the upper-left corner. These real numbers and are delimited using a single space character.

Binary format

A binary ESRI grid is stored in several files contained in at least two directories: the name directory and an info directory, where name has strict naming conventions.

References

Binary grid

• Arc/INFO GRID file structure
• AIG driver for GDAL

ASCII grid

• Format specification
• AAIGrid driver for GDAL