Digitising in GIS

Essentially digitising means making your own maps. In the early days of GIS this was the activity most GIS professionals were involved in. GIS labs were full of expensive equipment for converting paper maps into digital format by painstakingly drawing around the outlines of polygons and tracing lines. Most of this work has already been done, so we can use the results. However there is still a need for digitisation, particularly as things change on the ground or we may need to show specific elements of a site that have not been mapped already.

Digitisation results in new vector layers. Producing new raster layers is usually the result of classification, terrain analysis or raster algebra of some description. So we will produce ..

• Polygons
• Lines or ..
• Points

A vector layer consists of geometry and attributes. We can add attributes to the digitised layer later, but if the attributes are elements that we use for determining the boundaries of polygons or the elements of lines or points that we are looking at while digitising they should be captured along with the geometry. In the exercise you will be digitising vegetation types and use phase one mapping codes as a key attribute.

The minimum mappable unit (MMU) is a key element to define when digitising polygons. This is associated with the tradional cartographic concepts of scale. Think about digitising an area of forest. If the MMU has the same area as a single tree's canopy then there will be no concept of “open forest”. We would just draw around each tree. So defining the smallest area that we are prepared to draw around and classify is vital

A variety of maps could be used for guiding the digitising processs. or we could use ground truthing. Useful layers could be

• High resolution public domain satelite imagery
• OS and OSM maps
• Aerial photos

Your task is to digitise the area of Arne that we will visit on the field trip in order to produce a habitat map based on the general guidelines used in phase 1 mapping. You will be introduced to phase one habitat surveying in more detail on other units. To do this you need to ..

• Define an appropriate MMU for the area of interest.
• Intepret the available base maps appropriately
• Carefully follow the instructions and guidance for GIS usage supplied by Harry

Your digitised habitat map will be used in the assignment when you will look at differences between the habitats in a research context. So think carefully about the map as you produce it.

http://r.bournemouth.ac.uk:82/Quantitative_and_Spatial_Analysis/Week_1/export_to%20GeoJson/