Map Digitization

The process of representing an analogue signal or an image by a discrete set of its points is known as Digitizing. This data after conversion is in the binary format, which is directly readable by computer. The data to be converted can be a text, an image, audio or a video. The analogue signals are variable whereas the digital format is the discrete one. These discrete units are called as bits. These bits (8) organized in groups are known as byte. The digital signals are mainly represented in the form of sequence of integers. These integers can be converted back to analogue signal that are approximately similar to the original analogue signals. Digitizing is done by reading an analogue signal ‘A’, and at regular time intervals, representing the value of ‘A’ at that point by an integer.

Types of Digitizing:

Manual Digitizing: It is done using digitizing tablet. The operator manually traces all the lines from his hardcopy map and creates identical digital map on the computer. It is very time consuming and level of accuracy is also not very good. Heads-up Digitizing: It is similar to manual digitizing in the way that lines have to be drawn manually but directly on the computer screen. So in this level of accuracy increases and time taken decreases. Interactive tracing method: It is improvement over Heads-up digitizing in terms of speed and accuracy. Automatic Digitizing: It is automated raster to vector conversion using image processing and pattern recognition techniques. In this technique computer traces all the lines, which results in high speed and accuracy along with improved quality of images.

Device used for digitization is known as digitizer. It is an electromagnetic device consisting of a table upon which a map or a document to be scanned is placed. This device enters the spatial coordinates of mapped features from a map or a document to the computer. It is done with the help of a mouse or a hand held magnetic pen. The most commonly used digitizers are:

• Electrical orthogonal fire wire grid digitizer.
• Electrical wave phase type digitizer.

These digitizers can be supplied in various formats and are either in the form of a table or freestanding models with or without back lighting. A device known as “puck’ is used in cases where high degree of precision is required. It is made up of a coil embedded in plastic with an accurately located window with cross hairs. Digitizing of the coordinates is done, by placing cross hairs over them and pressing control button on the puck. The process of digitizing begins with the set of control points. At the later stages these points are used for converting the digitized map to the coordinates of the real world.