4.4.3.1 Geographic basemaps

Geographic basemaps may differ from regular plot axis in that some projections support a ``fancy'' form of axis and is selected by the BASEMAP_TYPE setting. The annotations will be formatted according to the PLOT_DEGREE_FORMAT template and DEGREE_SYMBOL setting. A simple example of part of a basemap is shown in Figure 4.6.

Figure: Geographic map border using separate selections for annotation, frame, and grid intervals. Formatting of the annotation is controlled by the parameter PLOT_DEGREE_FORMAT in your .gmtdefaults4 file.

The machinery for primary and secondary annotations introduced for time-series axes can also be utilized for geographic basemaps. This may be used to separate degree annotations from minutes- and seconds-annotations. For a more complicated basemap example using several sets of intervals, including different intervals and pen attributes for grid lines and grid crosses, see Figure 4.7.

Figure 4.7: Geographic map border with both primary (P) and secondary (S) components.