GIS MAPPING AND MODELLING

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EAST OF EDEN

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GIS MAPPING AND MODELLING CARRIE HOWARD The GIS component of the Suffolk Coast and Heaths Lifescapes project was undertaken using MapInfo v7, a windows based desk top GIS application. Extensive use was made of digital environmental base layers provided by Suffolk County Council including extensive use of their aerial photography, without which the effectiveness of the work would have been seriously reduced. The mapping and modelling work also benefited from the advice and guidance of a whole range of individuals (including national specialists) and local partners, to whom we are also very grateful. There were two main phases to the work which was initially planned to run over a two-year period. The first of these concentrated on identifying and mapping specific habitat types throughout the study area and digitising these into the GIS as polygons. A habitat polygon was simply a geo-referenced digital outline of the habitat to which information could then be attached in a database. The second phase of the project involved devising ways of identifying where it could be both feasible and desirable to create lost habitat in the wider countryside. Habitats were identified using a range of sources, but relied foremost on the interpretation of aerial photography. This was available at a high resolution for the whole of the study area and could be zoomed in to highlight specific areas of interest. Many habitats are highly distinctive from their hue, or from the texture or pattern of the vegetation that they contain. Areas that then met strict criteria (using guidance material developed by English Nature on identifying BAP habitats) were digitised and assigned as a specific BAP habitat type. A range of metadata was then associated with each polygon such as: the source used to locate the habitat (what led us to believe that it may be present), what scale the polygon was digitised at, and how sure we were of the determination. In some cases aerial photography was less reliable at determining habitats and so certain areas were supplemented with an element of ground truthing; where this was the case this was again recorded in the metadata. Extensive use was also made of the species records held at the SBRC database to identify habitat types since many habitat types are characterised by the species they contain. Individual and groups of species records could be laid over the aerial photography and used as a means for ‘homing in’ on likely habitat. Once all the habitat digitising was complete the second stage of the work could begin. Before individual habitat potential could be identified it was necessary to determine what the basic environmental requirements were in order to establish any given habitat. For example, to establish heathland a certain type of sandy soil is preferred, while grazing marsh can only really be established at below 10m elevation. The next stage was to develop a base layer of field polygons for the wider countryside where there was not currently any habitat (the majority of which was farmland or forestry). This involved digitising thousands of field boundaries so that the model we were constructing could apply a series of ‘rules’ to each field.

Trans. Suffolk Nat. Soc. 40 (2004)


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