3. DIGITIZATION OF GRAPHIC 
Digitization of graphic refers to the conversion of analog cartographic material to 
digital computer representation by the individual or combined means of 
electronic, optical, laser, solid state, or mechanical processes. The three most 
common forms are manual digitization, raster scanning and automatic line- 
following. Systems being used in the Branch are based on the first two 
techniques. 
3.1 Manual Digitization 
Manual digitizing systems are used for digitizing and editing in vector format. 
The hardware and software configuration of cartographic data capture systems 
using manual digitizing tables varies according to user's requirements and there 
are as many configurations as there are vendors. 
In the Branch, manual digitization is used to capture data from graphic overlays 
containing symbolized culture features, in support of the automatic digitizing 
system. 
Several interactive graphic workstations are equipped with a digitizing table as a 
working surface, The active area of the digitizing surface is 0.9 x 1.2 meters up to 
1.0 x 1.5 meters with a resolution of 25 micrometers and an accuracy of 
+ 75 micrometers. 
3.2 Automatic Digitizing (Raster Scanning) 
Raster scan digitization is the automatic process where point, line, and areal 
cartographic elements are converted to digital representation by means of 
electro-optical, solid state or laser cameras which traverse the manuscript in scan 
lines at prescribed resolution. 
Since early 1980's, raster scanners have been employed in several mapping 
agencies to expedite the process of converting map data from analog to digital 
form. The data produced by scanning represent a digital raster data structure 
which is entirely different from the vector data structure produced by manual 
digitizing and the digital stereo compilation system. 
Raster scanners convert the source document to a series of scan lines which 
contain grey tone values of the pictorial information on the scanned material. 
The values recorded depend on the scanner hardware, the input material and the 
shade of graphics work (colour, black-white and the optical densities sensed on the 
manuscript). 
In the Branch, raster scanning is performed on the SysScan (KartoScan) System, 
which is a stand-alone flat-bed scanner capable of accommodating graphics up to 
60 x 100 cm. The scanner records the grey-tone value of monochrome source 
documents, with a representation in the range from 1 to 127 for each pixel width. 
To save the storage space required for recording the grey-tone values, the scanner 
can record the captured data as a binary raster image. In addition, lines in which 
all pixels are white and strips which are totally white are not recorded. 
The scanner uses transmitted light to transduce graphic data recorded on 
transparent material or reflected light for opaque originals. The pixel size or 
resolution is variable and ranges between 25 and 200 micrometers. 
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