Digitizing

Digitizing is the process of converting data from analog to digital format. Digitizer is commonly used device to perform this task. A digitizer is electronics or electromagnetic device consisting a table upon the map or document can be placed. The most common types of digitizer currently used for mapping and high quality graphics are either the electrical orthogonal fine wire grid or the electrical-wave phase type. Both kinds of digitizer can be supplied in formats ranging from 11 inch X 11 inch to 40 inch X 60 inch, as table or free standing models with or without back lighting.

The coordinates of a point on the surface of the digitizer are sent to the computer by a hand held magnetic pen or a. simple device called a �mouse� or a �puck�. For mapping where considerable accuracy is required, a puck consisting of a coil embedded in plastic with an accurately located window with cross hairs is used. The coordinates of point are digitized by placing the cross hairs over it a pressing control button on the puck.

Digitizing usually begins with a set of control points, which are later used for converting the digitized map to real world coordinates. To digitizing point features each point is clicked once to record its location. Digitizing line or polygon features can follow either point mode or stream mode.