/*! \page gtk2_ex_geo Gtk2::Ex::Geo

\section index_geg_intro Gtk2::Ex::Geo modules

The Gtk2::Ex::Geo modules provide a plaform for developing geospatial
applications. The idea is to provide a canvas for geospatial data,
a set of dialogs, and glue code.

The tools build the abstract geospatial data layer defined by the
Geo::Layer module.

\section index_geg_glue Gtk2::Ex::Geo::Glue

A glue object manages the GUI. The dialog boxes of the registered
layer classes can be obtained from it. It maintains an overlay.

\section index_cli The CLI in an entry

The entry widget that is managed by a glue object is used for getting
commands from the user. The glue object maintains a history of the
objects. Old commands can be browsed with the arrow up and arrow down
keys. The user command is givent to Perl's eval function.

1) the variable names are inspected and found layer names are replaced
with pointers to real layers

2) keyword "focal:" in the beginning of an entry is removed and all
references to layers are replaced with clipped versions

3) commands p, plot, and inspect are recognized without explicit
reference to the Gtk2::Ex::Geo::Glue package

\section index_geg_dialogs Gtk2::Ex::Geo::Layer

The root class of all layer classes.

Layer classes should be registered with the glue object. The
registration information comprises a dialogs object (an instance of
DialogMaster or its subclass), and class methods it offers (typically
a subset of 'new', 'open', 'save', etc.).

\section index_geg_overlay Gtk2::Ex::Geo::Overlay

An overlay is a widget, subclassed from Gtk2::ScrolledWindow. An
overlay contains a list of layers, which it renders on a canvas, which
it puts into its window.

Rubberbanding and keyboard zoom-in (with + key), zoom-out (with -
key), and panning (with arrow keys) is built-in.

\section index_geg_dialogs Gtk2::Ex::Geo::Dialogs

*/