attribute column; if missing, the first
column is taken; a name or a column number may be given
na.value
numeric; value given to missing valued cells in the
resulting map
...
arguments passed to write.table, which is used
to write the numeric data
Value
read.asciigrid returns the grid map read; either as
an object of class SpatialGridDataFrame-class or, if
as.image is TRUE, as list with components x, y and z.