Heads-up digitising and interactive tracing

Heads-up digitisation, or on-screen digitisation, is a very commonly used method of digitisation. It is similar to manual digitisation except that the base map or image is already in a digital raster form. The term 'heads-up digitisation' is used because the attention of the user is focused up on the computer screen and not on a digitisation tablet.

The main idea of this type of digitisation is to convert the digital image into a form usable in the GIS environment (i.e. in a form such that each feature on the map has a geographic co-ordinate associated with it).

The first step is to convert the paper maps or images into a digital form, which is accomplished using a scanner. A scanner automatically captures map features, text, and symbols in the map as individual cells, or pixels, and produces an automated digital image in raster format.

However, this raster image lacks any geographic information; this has to be input manually. In order to achieve this, the digital image is displayed on the screen and zoomed to a comfortable level such that all the features on the digital image can be easily traced out on the screen itself to create new layers or themes. This process is called ‘interactive tracing’.

Related methods include: 2d Modelling – raster, 2d Scanning, Geo-referencing and projection, Overlaying and Photogrammetry.

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