Describe digital techniques of mapping.

Digital techniques of mapping consist of following operations:

(i) Data Capture or Data Acquisition : Data about real world can be acquired from various sources. Field observations by traditional methods like aerial photos, GPS (Global Positioning System), satellite imageries, old existing maps and field manuscripts record properly verified are some of them. The field record maps and aerial photos are converted into digital form through scanning and digitisation, which can be processed further according to needs.

(ii) Geo-coding of Geo-Referencing of Roster Image : Scanned roster images and satellite imageries are corrected for distortions by matching them with Ground Control Points (GCPs) occurring in an image. GCPs are features

of known ground location that can be accurately located on the aerial photo or satellite imagery. GCPs are located both in terms of their image coordinates (columns and row numbers) on the distorted image and in terms of their ground coordinates. A least-square regression analysis is done to interrelate the geometrically correct (map) coordinates and distorted image coordinates. Then image is worked to have correct geometrical relationship with its corresponding ground situation.

(iii) Digital Fair Mapping : Geo-Coded roster image is used as a back drop to draw point-features, line features and aerial features and annotate them with proper symbols and text. Alternatively, the above features or the roster image may simply be digitized without using symbols to create cartographic data base. The

digital map may be subjected to automated cartographic processes, like generalisation, classification, etc.

(iv) Map Reproduction: The digital maps prepared through digitization of roster image in computers is used either to generate colour separates on paper or film through printer or it may be used to prepare colour composites on films through printer, or it may be used to prepare colour composites on films through printer, or it may be used to prepare colour composites on films for each colour e.g. cyan (c), magenta (m), yellow (y) and black (k). The colour separate on a paper or films are photographically merged to generate the colour composites. These colours are used to prepare plate for offset printing.