GIS Files 3: Adding real-world information

3.5: Structured GIS data is the key (1)

The significance of structure

For geospatial data to be really useful to GIS applications it must be structured to model the real world. What is the significance of structured data?

In the last few pages we have seen that there are a number of ways of getting general types of information about objects into a GIS. This always relies on the presence of a layer storing the location of a set of objects along with some attribute like a name or an ID number.

Our examples so far show that:

1. to link environmental information about rivers we needed a river map layer possessing names as attributes; and

2. to geocode a set of addresses we needed a geographic layer with the coordinates of postcode locations together with the postcode text itself.

In these examples the GIS must hold location and attribute data that corresponds to the physical objects which people want to analyse. This means that the structure of the physical object data in the GIS data must be attuned to the types of application that the system is meant for.

In the rivers example this is achieved because the data to be analysed relates to simple large objects (whole rivers) for which there are many sources of suitable small-scale GIS data. However, when attempting to look at information about much smaller objects, like single addresses or buildings, the geographical data must be much more detailed and structured so that the appropriate information for actual objects is present. Because most large-scale data available for use in GIS has come from digitised cartographic sources, the data structure is not necessarily optimised for GIS analysis. This is a very important point, and the way in which Ordnance Survey is re-engineering its large-scale database for OS MasterMap™ developed from DNF™ illustrates the significance of structured data.

Don't worry, this will all become clearer as we move through this chapter and the next. The idea is that data has to be structured in a certain way to carry out certain types of spatial analysis.

We will now look at Ordnance Survey point data that is often used for geocoding and Ordnance Survey road network data that is often used for analysis of networks.

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