The modern era witnessed a change from paper maps to digital maps. As geo spatial technology evolved to the present day status, more and more paper maps have turned into digital maps. The availability of cartographic symbology, in major global GIS software has made it possible to prepare digital maps. There are different kinds of GIS digital mapping. Most common ones are conversion of paper maps to digital form and digitization from satellite images and other images using image interpretation techniques. In case of paper maps to digital map conversion, scanning of the paper maps is a necessary prerequisite. Scanning can be done to a 300 dpi level to get clarity of the features to be mapped. Then the images will be geo referenced. Geo referencing can be done using ground control points taken either from other reference maps, coordinate values printed on the maps, or though DGPS survey. During geo referencing, the map is projected to user defined coordinate systems and projection. All GIS software is having almost all of the world’s coordinate systems, projections and datum in the form library files. Once the maps are in real world coordinates, the digitization can be done using on screen heads up digitization or using a digitization table.
There are three entities in which any GIS mapping services accept the features. These are points, lines and polygons. Features like land marks, bus terminus, tube wells etc can be depicted in the form of points. Lines are loci of points with and start point and an end point. Road network, railway lines etc are usually depicted in the form of lines. Polygons are lines with start point and end points are same. Water bodies, settlements, parcel boundaries etc are usually depicted in the form of polygons. Once the features are extracted digitally in the form of points, lines, and polygons, various cartographic symbology and colors can be assigned to these features. Size and styles of features can also be incorporated at this stage to the maps. Another important advantage of digital mapping is incorporation of the attributes. Descriptions and information regarding the points, lines and polygons can be in the form of any number of attributes. In a GIS mapping, these attributes will be defined through a data base structure. Main kinds of mapping services are for geological mapping, base mapping, land use land cover mapping etc. Land parcels in the form of cadastral maps can also be prepared in this way. Administrative boundary maps, forests boundary map are also digital maps prepared in this way. Remote sensing data products such as satellite images of varying resolutions and aerial photographs are major input for preparation of digital maps. These images can be interpreted using interpretation keys such as tone, texture, association, size, shape and pattern. Useful feature extraction thus derived will be filled with attributes and then cartographic layout can be prepared to get a ready to print maps. During this process, required scale, north arrow and legend will be prepared. Overall layout map will be placed in a spatial frame work of coordinates on suitable paper size to get a ready to print lay out maps which can be exported desired formats such as jpgs and pdfs.
