Whether it contains vectorial or raster data, every map
exists as a set of data. In addition to this data set, a map is characterized
by a set of properties and a theme. Every map has a theme, and in JViews Maps for DefenseJViews Map Viewer a theme specifies the layers, zoom
levels, and other information that control how the map is viewed at
different zoom levels. A theme is the sum of the characteristics of
a map.