The process of converting data from analog to digital format is known as
digitizing. The device used for this purpose is called digitizer. It is an
electronics or electromagnetic device consisting of a table upon which map or document can be placed. The electrical orthogonal fine wire grid and the electrical-wave phase type digitizer are the two most commonly used digitizers. These can be supplied in various formats ranging from 11 inch x 11 inch to 40 inch x 60 inch. These are either in the form of a table or freestanding models with or without back lighting.
A mouse or a hand held magnetic pen is used to send the coordinates of a point on the surface of the digitizer to the computer. In cases like mapping where high degree of accuracy is required a device known as 'puck' is used. It consists of a coil embedded in plastic with an accurately located window with cross hairs. Digitization of coordinates is done by placing the cross hairs over it and pressing the control button on the puck.
Digitizing begins with set of control points, which at the later stages are used for converting the digitized map to the coordinates of the real world. To digitizing point features each point is clicked just once and is location gets recorded. Digitizing line of polygon features can follow any of the two modes namely the point mode or stream mode.
