Data is a fundamental component of GIS. Without it Geographic Information Systems would simply be a software application within built spatial analysis algorithms. Data and understanding data is the key to any successful GIS platform integration or project. Where does data come from?

Licensed data

In commercial applications datasets can be licensed from the persons or organisation which own the IPR to that data. i.e. who created it. In the GIS arena some common suppliers of licensed GIS datasets include the Ordnance Survey (more on them later), Environment Agency, British Geological Survey, English Heritage and Countryside Council for Wales to name a few. In order to use licensed data you need to arrange the supplier the most appropriate licensing framework for the intended use of the data. Licensing can be complicated and challenging to organise but with a little perseverance you can get the contracts you need to use the data. It is very important to use any data as it is intended and within the confines of the licensing agreement. Any deviation from this is not only illegal but could jeopardise future dealings.

Open source data.

There is an ever increasing amount of freely available datasets available. These vary in usefulness and quality. One of the biggest shifts in data procurement in recent years has been the opening up of Ordnance Survey data. A large swathe of Ordnance Survey digital mapping is now free to use and crucially this also applies to commercial applications. Currently this does not include any of the “MasterMap” products but nevertheless is very useful especially to companies looking to implement a GIS for the first time or on a limited budget.
The sources of data we have looked at above are what is called secondary data. I.e. it already exists and you only need to acquire it. What happens if you the data you need is nonexistent or unique to your organisation and projects? For example you may have paper maps delineating parcels of land. In this situation you need to go through a process of primary data collection where you create a dataset by converting the paper maps into a digital GIS friendly format. This is called digitisation.

Paper maps are still an important source of Geographic Information and it is important to remember a few fundamental concepts. Maps are generalisations of reality. They are abstract and a model of physical (usually) features on the earth’s surface. This is an important consideration as generalisations in the paper map are likely to be inherited into the created dataset. Projection of the map is also important. Since the earth is a 3D mass (geoid) and maps are 2D constructs some form of translation process is undertaken in a process known as map projection. For now we won’t look any more at these complex subjects as they will be revisited in later articles.

Digitising

As mentioned above the process of digitising is concerned with capturing data from paper documents. Digitisation quality is dependent on the quality of the source material (maps) and a study of the source material quality should always be the starting point in a digitisation project.
The most common and modern method of digitising is through something called “heads up” digitising. In this process the source maps are scanned (to become raster images) and then displayed on screen (hence “heads up”). An operator can then trace around any feature he or she is trying to collect.

This is a very short summary of types of GIS data sources. The process of data capture is complicated and with the potential for error propagation at many stages.