Mapping the Universe - Mapping Scientific Frontiers: The Quest for Knowledge Visualization - page 48

Fig. 2.1 Scenes in the film Powers of Ten (Reprinted from http://www.powersof10.com/film
© 2010 Eames Office)
the purpose is to show a variety of features of the world or a region, such as
coastlines, lakes, rivers, and roads. In history, the reference map was prevalent until
the middle of the eighteenth century. The knowledge of the world was sharply
increasing and cartographers were pre-occupied with making a world map that
would be as comprehensive as possible. Thematic maps, on the other hand, are
more selective and they display the spatial distribution of a particular geographic
phenomenon. Thematic maps are also known as special-purpose, single-topic, or
statistical maps. Thematic maps emerged as scientists turned their attention to the
spatial attributes of social and scientific data, such as climate, vegetation, geology,
and trade. A thematic map is designed to demonstrate particular feature or concepts.
The purpose of thematic maps is to illustrate the structural characteristics of some
particular geographical distribution. A thematic map normally focuses on a single
theme.
Thematic maps came late in the development of cartography. Thematic maps
make it easier for professional geographers, planners, and other scientists and
academicians to view the spatial distribution of phenomena. Thematic maps were
not widely introduced until the early nineteenth century. The last 30 years have been
referred to as the “era of thematic mapping,” and this trend is expected to continue
in the future.
Every thematic map has two important components: a geographic or base map
and a thematic overlay (See Fig. 2.2 ). A geographic base map provides information