doc: Use lowercase for 2D raster mask (#4401)

On many places (more than covered here), 2D raster mask is called MASK conflating the concept (mask) and the implementation (MASK raster). Users using the r.mask tool may not interact with the underlying raster directly, so there is no reason to use MASK over mask.

This is changing MASK to mask and modifies related wording. However, this is also leaving many places as they are with MASK. Some will be better revisited with or after #2390 and #2392 when a more comprehensive solution is available.

This fixes and keeps in sync wording in r.null and r.external, and moves r.circle comment documenting the interface to a flag description.

display/d.histogram/d.histogram.html

@@ -10,7 +10,7 @@ <h2>DESCRIPTION</h2>
 <h2>NOTES</h2>
 
 <em>d.histogram</em> respects the current geographic region settings
-and the current MASK (if one exists).
+and the current raster mask (if mask is active).
 
 <p><em>d.histogram</em> uses the colors in the map's color look-up table
 (i.e., the map's <em>colr</em> or <em>colr2</em> file).

raster/r.circle/main.c

@@ -79,7 +79,9 @@ int main(int argc, char *argv[])
 
     flag = G_define_flag();
     flag->key = 'b';
-    flag->description = _("Generate binary raster map");
+    flag->label = _("Generate binary raster map");
+    flag->description =
+        _("Generate binary pattern only (useful for creating mask)");
 
     if (G_parser(argc, argv))
         exit(EXIT_FAILURE);
@@ -114,7 +116,7 @@ int main(int argc, char *argv[])
                         "using the binary flag"));
 
     if (flag->answer)
-        binary = 1; /* generate binary pattern only, useful for MASK */
+        binary = 1;
     else
         binary = 0;
 

raster/r.external/r.external.html

@@ -17,10 +17,12 @@ <h2>NULL data handling</h2>
 NULL cells are those whose value matches the value reported by the
 GDALGetRasterNoDataValue() function.
 
-To apply the GDAL-linked the user need to either create a MASK (e.g.
-with <em>r.mask</em>) and then "apply" it using e.g. <em>r.resample</em>,
+<p>
+To introduce additional NULL values to a computation based on a GDAL-linked
+raster, the user needs to either create a mask with with <em>r.mask</em> and
+then "apply" it using e.g. <em>r.resample</em> or <em>r.mapcalc</em>,
 or use <em>r.mapcalc</em> to create a copy with the appropriate categories
-changed to NULL (if() condition).
+changed to NULL (<code>if()</code> condition).
 
 <h2>EXAMPLES</h2>
 

raster/r.null/r.null.html

@@ -49,10 +49,12 @@ <h3>External maps</h3>
 From the <a href="r.external.html">r.external</a> documentation: GDAL-linked
 (<em>r.external</em>) maps do not have or use a NULL bitmap, hence <em>r.null</em> cannot
 manipulate them directly. Here NULL cells are those whose value matches
-the value reported by the GDALGetRasterNoDataValue() function. To apply the
-GDAL-linked the user need to either create a MASK (e.g. with <em>r.mask</em>) and
-then "apply" it using e.g. <em>r.resample</em>, or use <em>r.mapcalc</em> to create a copy
-with the appropriate categories changed to NULL (<tt>if()</tt> condition).
+the value reported by the GDALGetRasterNoDataValue() function.
+To introduce additional NULL values to a computation based on a GDAL-linked
+raster, the user needs to either create a mask with with <em>r.mask</em> and
+then "apply" it using e.g. <em>r.resample</em> or <em>r.mapcalc</em>,
+or use <em>r.mapcalc</em> to create a copy with the appropriate categories
+changed to NULL (<code>if()</code> condition).
 
 <h2>EXAMPLES</h2>
 

raster/r.stream.extract/r.stream.extract.html

@@ -126,7 +126,9 @@ <h3>Defining a region of interest</h3>
 
 The stream extraction procedure can be restricted to a certain region of
 interest, e.g. a subbasin, by setting the computational region with
-<em><a href="g.region.html">g.region</a></em> and/or creating a MASK. Such region of interest should
+<em><a href="g.region.html">g.region</a></em> and/or creating a mask
+with <em><a href="r.mask.html">r.mask</a></em>.
+Such region of interest should
 be a complete catchment area, complete in the sense that the complete
 area upstream of an outlet point is included and buffered with at least
 one cell.

raster3d/raster3dintro.html

@@ -115,7 +115,7 @@ <h4>Conversion from 2D raster maps</h4>
 2D rasters are considered as slices in this case and
 merged into one 3D raster map (<a href="r.to.rast3.html">r.to.rast3</a>).
 
-<h3>3D region settings and 3D MASK</h3>
+<h3>3D region settings and 3D mask</h3>
 
 GRASS GIS 3D raster map processing is always performed in the current 3D region
 settings (see <a href="g.region.html">g.region</a>, <em>-p3</em> flags), i.e.

scripts/r.out.xyz/r.out.xyz.html

@@ -6,7 +6,7 @@ <h2>DESCRIPTION</h2>
 <h2>NOTES</h2>
 
 This module will by default not export x,y coordinates for raster cells
-containing a NULL value. This includes cells masked by a raster MASK.
+containing a NULL value. This includes cells masked by a raster mask.
 Using the flag <b>-i</b> also these raster cells will be included in the
 exported data.
 <p>