Geography Reference
In-Depth Information
NODATA_VALUE -32768
21 22 21 23 23 23 23
21 25 25 25 25 25 25
21 25 23 23 23 24 24
29 27 25 23 23 26 26
25 27 29 26 27 23 23
27 27 27 21 21 23 23
Minimize, but do not close, Forty_Two_Cells.txt.
We haven't defined a coordinate system for our raster, so a standard Cartesian system will be assumed.
In the text file, the meanings of NCOLS and NROWS are obvious. XLLCENTER is the x-coordinate of the
center of the cell in the lower-left corner. YLLCENTER is similar. CELLSIZE is the length of a cell side.
The NODATA_VALUE can be set to whatever you want. Obviously, it would be a real mistake to set it as a
number that might actually be found in your data. Here, it is set to be able to hold the smallest number
that can be represented by a 2-byte (16-bit) integer. (For reference: that number is -32,768.) The numbers
following the first six lines are the values the cells are to take on, in “row-major order”—meaning all the
values on the first row, followed by all the values on the second row, and so on. The lines in the text file do
not have to correspond to the rows in the raster.
(By the way: Only the order of the numbers prescribing the values of the cells is important. That is, the file
NCOLS 7
NROWS 6
XLLCENTER 4150
YLLCENTER 1150
CELLSIZE 100
NODATA_VALUE -32768
21 22
21 23 23 23 23 21 25 25 25 25 25 25 21 25 23
23 23 24 24
29 27 25 23 23 26 26 25 27
29 26 27 23 23 27 27 27 21 21 23 23
would work just as well.)
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