All the maps contained in this Atlas, have been produced using a technology known as Geographic Information Systems or GIS for short.

A GIS can be defined as a specialised computer system (both hardware and software) for capturing, storing, checking, merging, manipulating, analysing and displaying data which can be located somehow on the surface of the Earth. In geography, the term “spatial” is used when referring to such data. Latitude and longitude coordinates, map references, administrative regions, water bodies and settlements are some of the means of relating information to a particular location. In this respect, a GIS is different from a Computer Aided Design programme (CAD) that stores information on features in an abstract space.

Real world features such as roads, rivers, soil types, or water quality sampling sites are represented in a GIS in digital form as points, lines (arcs), polygons (areas) or as cells (a grid).

Descriptive information or attributes about objects (e.g. names, ownership, depth, soil type) can be associated with the geographical data. This “descriptive” information is normally stored in the form of tables in a database and is linked to the geographic or map data by a common identifier.

For the most part, spatial data can be "re-projected" from one coordinate system into another, thus data from various sources can be brought together into a common database and integrated using GIS software. In this way, a global database on rare birds using latitude and longitude to mark sightings of particular species could be combined with data on river networks compiled on the basis of maps using the Spanish national coordinate system. Spatial data and associated attributes in the same coordinate system can viewed together and layered on top of each other to create maps.

Another property of a GIS database is that it has “topology”. This term defines the spatial relationships between different features. When topological relationships exist, analyses such as modelling the flow through connecting lines in a network, combining adjacent polygons that have similar characteristics and overlaying geographic features can be performed.

Higher level analysis can also be carried out on data. Questions such as “What would happen if…pollution accidentally leaked into a river?”, “Where does…a Podzol occur next to arable land?” or “Is there a pattern to…burglaries in a city?” are only feasible on large volumes of information by using a GIS.

Other examples of analysis that have been carried out using GIS software range from identifying houses on flat land that are within 200m of rivers for flood predictions to locating groundwater regions under permeable soils to limit pesticide applications.

The last, but by no means least, component of a GIS is the human element! Well-trained people, knowledgeable in spatial analysis and skilled in using GIS software are essential to the GIS process.

Increasingly, GIS are being used by more and more organisations. Originally developed primarily as a research tool for Geography departments of universities, now GIS is widespread in facilities management (e.g. water pipes, electricity cables), marketing and retailing (e.g. optimising store location with respect to customer needs), military (e.g. battlefield maps, terrain evaluation), environmental (e.g. predicting floods, erosion risk, forest fires), transport (e.g. vehicle routing, noise surveys), health (e.g. relationship between illnesses and social or environmental factors) and many, many more cases.

The GIS software used in the production of the maps in this book was a product called ArcGIS developed by ESRI Inc. from Redlands, California.

If you would like to learn more about spatial data and Geographic Information Systems then have a look at the following sites on the World Wide Web;

• http://www.ec-gis.org/inspire/
• http://www.eurogi.org/

• http://www.gis.com
• http://www.geo.ed.ac.uk/home/giswww.html
• http://www.usgs.gov