The File-Open Menu Option

This choice allows you to open a raster map for editing.  You
will be presented with a list of the raster maps that are in 
your @ref("mapset search path",16.glossary/srchpth.def) (in an xgbrowser dialog) so that you 
may choose a map to edit. 

When you open a raster map for editing you must decide what 
@glossary("region",16.glossary/georeg.def) is to be used.  At the bottom of the dialog you will 
see two toggle buttons; one reads "Use raster map's region" 
and the other reads "Use current region."  The default choice 
is to use the raster map's region, which allows you to edit 
the entire raster map.  

If you choose to use the current region, on the other hand, 
then you will edit only the portion of the raster map that 
falls within the current region.  Additionally, you will be 
editing the raster map as if it has the same grid-cell size 
as the current region.

When you open a raster map for editing the raster map the
raster-editor must will first copy the raster map into a
@ref("segment file",xgre/def_segfile).  If you open a very large raster map it may 
take a minute or so to convert it to a segment file.

The file name of the new segment file that is created will be
based on the name of the original raster map.  Because you may
create more than one segment file for one raster map, a special
file extension or suffix is added to the segment file name.
The first segment file that you create for a raster map will
have the suffix ".s0", the second will have the suffix ".s1",
the third will have the suffix ".s2" and so on.

