Improve frame example (#16)

Author: Esteban82

docs/tutorials/basics/frames.rst

@@ -1,5 +1,5 @@
 Frames, ticks, titles, and labels
------------------------
+---------------------------------
 
 Setting frame, ticks, title, etc., of the plot is handled by the :gmt-module:`-B <basemap#b>` parameter that most plotting modules contain like :gmt-module:`basemap`.
 
@@ -10,14 +10,14 @@ By default, GMT does not add a frame to your plot. For example, we can plot
 the coastlines of the world with a Mercator projection:
 
 
-.. gmtplot::
+   .. gmtplot::
 
-   gmt begin frames png
-      gmt coast -R-180/180/-60/60 -JM25c -W
-   gmt end show
+      gmt begin frames png
+         gmt coast -R-180/180/-60/60 -JM25c -W
+      gmt end show
 
 
-To add the default GMT frame style to the plot, add **f** to the :gmt-module:`-B <basemap#b>`.
+To add the default GMT frame style to the plot, add ``f`` to the :gmt-module:`-B <basemap#b>`.
 
 
    .. gmtplot::
@@ -29,9 +29,9 @@ To add the default GMT frame style to the plot, add **f** to the :gmt-module:`-B
 
 
 Tick labels
-~~~~~~~~~~
+~~~~~~~~~~~
 
-In GMT the tick labels are called annotations. Add them by passing **a** through the :gmt-module:`-B <basemap#b>` parameter:
+In GMT the tick labels are called annotations. Add them by passing ``a`` through the :gmt-module:`-B <basemap#b>` parameter:
 
    .. gmtplot::
 
@@ -45,7 +45,7 @@ In GMT the tick labels are called annotations. Add them by passing **a** through
 Gridlines
 ~~~~~~~~~~
 
-Add automatic grid lines to the plot by adding **g**:
+Add automatic grid lines to the plot by adding ``g``:
 
 
    .. gmtplot::
@@ -56,10 +56,24 @@ Add automatic grid lines to the plot by adding **g**:
       gmt end show
 
 
+Custom annotations and intervals
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+To adjust the step widths of annotations, frame, and grid lines we can
+add the desired step widths after ``a``, ``f``, or ``g``. In the example
+below, the step widths are set to 30°, 7.5°, and 15°, respectively.
+
+   .. gmtplot::
+
+      gmt begin frames png
+         gmt coast -R-180/180/-60/60 -JM25c -W
+         gmt basemap -Ba30f7.5g15
+      gmt end show
+
 Title
-~~~~~~~~~~
+~~~~~
 
-The figure title can be set by passing **+ttitle**:
+The figure title can be set by passing ``+ttitle``:
 
    .. gmtplot::
 
@@ -68,3 +82,16 @@ The figure title can be set by passing **+ttitle**:
          gmt basemap -Bafg
          gmt basemap -B+t"Mercator Map"
       gmt end show
+
+Subtitle
+~~~~~~~~
+
+Then you can add a subtitle with ``+ssubtitle``:
+
+   .. gmtplot::
+
+      gmt begin frames png
+         gmt coast -R-180/180/-60/60 -JM25c -W
+         gmt basemap -Bafg
+         gmt basemap -B+t"Mercator Map"+s"Subtitle"
+      gmt end show