Any successful example of GIS is based on two fundamental components:
- the map data; and
- the computer software to perform calculations and analysis.
There are many different organisations producing data for use in GIS; Ordnance Survey is just one of these. There is also a large industry in GIS software with hundreds of companies producing thousands of products.
To be a truly effective system, a GIS needs good software and good data. One without the other will not be productive. The other vital component is people. The GIS will only provide useful answers to problems if the user is able to ask the right questions and can interpret the results.
A GIS can be a simple desktop software package costing a few hundred pounds, running on a standalone PC. Alternatively a single system can involve a very large network of workstations and servers with many different software components costing millions of pounds.
The evolution of GIS
The story of GIS begins in the world of maps. A map is a simplified visual representation of real things from the real world. Maps can model the world in more than one way:
- A topographic map shows the physical surface features, for example roads, rivers and buildings.
- A contour map shows lines which connect point locations at which a certain property has the same value, for example height above sea level and isobars showing air pressure.
- A chorochromatic map shows areas characterised by some general common feature, for example political maps and agricultural crop types.
GIS applications have evolved from a combination of two well-established types of software: the way in which map geometry is handled is based on graphics and computer-aided-design (CAD) technology; the way in which attribute information is handled has been developed from conventional spreadsheet and database technology.
A professional GIS user must be able to understand the disciplines of both these types of software, as well as appreciating geographic principles.
One of the historical drawbacks to GIS has been the high cost involved. Nowadays reduced costs are making GIS more accessible. The Internet is also playing a big part in increasing the extent to which GIS technology is being utilised. Many web sites use some underlying GIS processing to present customised map images to your browser.
Data sources - map data
The map is actually a very sophisticated information source. The human eye is able to interpret a rich amount of information from a map simply from the pictorial content. This is enhanced by the use of textual annotations (names of objects are written on a map in such a way that the letters do not get in the way of the geographical features themselves). GIS works by taking all of this information and recording it in electronic form.
Look at any map – the different shapes and symbols are used to illustrate features. There are four main types of symbol used to depict the different feature types. In fact, all map features can be divided into one of four different categories:
- Point (for example, a cross symbol to represent a church).
- Line (for example, a yellow line to represent a road).
- Polygon shape or Area (for example, a blue area to represent a lake).
- Text (for example, the name of a building).
The most common form of GIS data is based on topographic features – that is, the features that make up the physical structure of the land surface. Topography includes the relief of an area (the shape of its surface) and the position of both natural and man-made features.
In addition to topographical data, there are more diverse sources of information that can be linked into a GIS.
Aerial view of the Eden Project in Cornwall
Large amounts of data relating to both people and the environment can be viewed and analysed in a GIS. The image above shows how a layer of environmental information can be overlaid on a map backdrop.
Even aerial and satellite imagery can be incorporated into a GIS and viewed along with other data for the same area, as long as the ground extent of the image can be identified. The most powerful GIS applications use data taken from a range of different sources.
Ordnance Survey data and GIS
Ordnance Survey produces many different GIS data products – the diversity of these products is itself an indication of the many different ways in which GIS can be used. They range from simple raster images of road atlas style mapping, to very detailed vector data extracted from the National Topographic Database, which is Great Britain's official archive of large-scale mapping. This database is incredibly detailed – it shows every house, every fence, and every stream in every single part of Great Britain.
Click through the product list below to get an idea of the range of different types of product available for GIS use.
- 1:250 000 Scale Colour Raster
- OS MasterMap Integrated Transport Network Layer
- 1:50 000 Scale Colour Raster
Not all data in a GIS will look like a map. At first glance the sea of dots in the image may not appear particularly useful: ADDRESS-POINT is not a cartographic product, but is designed to be used in conjunction with other layers of information within a GIS application.
ADDRESS-POINT can be used to identify specific properties against a map backdrop or to link to other sources of associated information, like voting wards. Linking information in this way is explained more fully in later section of the GIS files.