Bathymetry and Acoustic Backscatter—Elwha River Delta, Washington

Appendix

Appendix. ESRI ASCII Grid Format

To import ASCII grids into common GIS packages:

ArcGIS: Use ArcTools's Import ASCII to Grid function
ArcView: Use the import ASCII Grid function (May need Spatial Analyst)
GRASS: Use the 'r.in.arc' function.

The ASCII file consists of header information containing a set of keywords, followed by cell values in row-major order. The file format is:

<NCOLS xxx>
<NROWS xxx>
<XLLCENTER xxx | XLLCORNER xxx>
<YLLCENTER xxx | YLLCORNER xxx>
<CELLSIZE xxx>
{NODATA_VALUE xxx}
row 1
row 2
.
.
.
row n

where xxx is a number and the keyword nodata_value is optional and defaults to -9999. Row 1 of the data is at the top of the grid, row 2 is just under row 1 and so on. The nodata_value is the value in the ASCII file to be assigned to those cells whose true value is unknown. In the grid they will be assigned the keyword NODATA. Cell values are be delimited by spaces. No carriage returns are necessary at the end of each row in the grid (although they are included in this case). The number of columns in the header is used to determine when a new row begins. The number of cell values is equal to the number of rows times the number of columns.

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