An introduction to digital mapping

GIS and Forestry

There are a number of advantages to using digital mapping in forest management planning:

• It provides a straightforward way of producing attractive customised maps;
• It allows many different sources of information to be displayed and combined;
• Digital maps can be integrated with spreadsheets and databases to map the outcomes of plans and predictions.

There are a number of different mapping and GIS (geographic information system) programmes available. Two of the most widely used, MapInfo and ArcView are conceptually similar and can do many of the same things. However, they have different file formats so you may need to translate data into the right format before it can be used. In this tutorial we will use MapInfo (version 5.5). One attractive feature of MapInfo is that you don’t need to be a GIS expert to produce attractive and informative maps.

An introductory guide to MapInfo has been written by Nigel James and is available on the Bodleian Library web site.

Layers

The key to GIS is that data is displayed in separate layers. You can open several layers simultaneously and see their data in a single map. Layers can be built up to show patterns that are not apparent on a single map. For example you could open a soil map at the same time as a map showing species composition of forest stands. You could use the combination map to investigate which tree species are found growing on a particular type of soil. The base map is the layer onto which you add further information. In this tutorial we will use an Ordnance Survey map of Little Wittenham as our base map.

In MapInfo the data that is shown in a layer is stored in a table. Table files can also contain other things including data that is not mapped and a special layer, known as the cosmetic layer on which you can draw new map objects, label, analyze etc.

Sources of data

Useful datasets for forest resource mapping can be bought, downloaded for free from the web or you can create them yourself. In this tutorial you will gain experience of all three sources.

Ordnance Survey data

The base map for this tutorial is Land-Line Plus data from the Ordnance Survey. This has been digitised from Ordnance Survey Large Scale (1:2,500 in rural areas) maps. The maps show the accurately surveyed positions of both natural and man-made features. At present (Febuary 2002) a 1 km by 1 km Land-Line Plus tile costs less than £20 to purchase. Whilst you are a student at this University you can register to access this and other OS digital map data for free via DIGIMAP at  Edinburgh Data and Information Access (EDINA), a national data centre. It offers the UK tertiary education and research community networked access to a library of data, information and research resources.

A major disadvantage of Land-Line Plus maps is that objects have not been digitised as polygons but as a series of lines, defining their boundaries. In MapInfo a polygon can be selected for analysis or display. A woodland, for example could be selected to calculate its area or shaded according to its species composition on a thematic map. With Land-Line data, however, only the boundaries can be selected. Land-Line is soon to be replaced by a new system called MasterMap in which every feature (including woods, fields, buildings and even post boxes) on a map is a unique numbered object. MasterMap will be available via EDINA shortly.

The OS supply their data in different formats. National Transfer Format (NTF) is a nationally agreed standard for the transfer of geographical data. It is administered by the British Standards Institution. It is now the standard format for Ordnance Survey digital data. Unfortunately NTF files cannot be opened directly in MapInfo but need to be translated into MapInfo Interchange Format (MIF).  In order to shortcut this process I have downloaded the data, translated it and imported the files into MapInfo. All you need to do is open them!

English Nature data

Another important source of forestry data for the UK is English Nature. Their digital boundary datasets have been made freely available via their website. Maps of Sites of Special Scientific Interest (SSSIs), National Nature Reserves (NNRs), Special Areas of Conservation (SACs), Special Protection Areas (SPAs), Ramsar sites, and Ancient Woodlands are all available in MapInfo format.