Draft operational guidelines of digital india land records modernization programme (dilrmp) introduction

2.6 Feature abstraction from the grid-corrected scanned cadastral images

2.6.1 Template creation: Before starting the vectorization, a standard template has to be created. In the template, the layer name, line type, color and thickness for each feature (e.g., parcel, roads, canals, river, etc.) present on the map is standardized. Different graphical representation (symbol-alamats) in the map is to be standardized as point features with proper layer name, symbol and colour. This maintains uniformity in all the map outputs. The template also holds various mathematical grids, graphical scales, and other map features like north arrow, boundary lines, headings and other permanent annotations. A symbol library is created, which contains the various symbols shown in a village map. The symbol library gets depicted in the legend of the template. The main intention behind this is to maintain the uniformity over all the village maps that are digitized. The template should also address the font type of the annotation in the maps. Generally, UNICODE system is adopted with proper font for depicting the local language script. However, the template standards may vary from State-to-State and have to be regenerated with changes in the input specifications.

2.6.2 Feature abstraction is the process of capturing the point, line, and polygon features as vectors and text as annotation. The grid-registered scanned cadastral map sheet is displayed in the background, the required environment settings for digitization are set, and the required features are captured into different layers (based on the feature type). During digitization, attributions to the features will also be done. Only heads-up manual digitization should be carried out. Auto-vectorisation should not be attempted. Error should be within permissible limits for digitization, viz., weed tolerance, coordinate movement tolerance, sliver polygon tolerance, coordinate unit, planimetric errors, fuzzy tolerance, etc.

2.6.3 The uniformity in layers, line type, color, annotation, etc. during digitization will be maintained by using the template, as described above, to capture all the features in their respective layers. The final output of this process will be a digital map which will be a true copy of the paper map, along with necessary legends, scale bar, north arrow, borders, etc.

2.6.4 Once the digitization process is over, the DQC-4 is performed. This process assures the features abstracted from the scanned map sheets are true in its type (i.e. point, line or polygon), accurate in location and its attributes. Tag should be maintained wherever the feature/annotation could not be read along with null and duplicate errors. The errors have to be reported in the draft output map, which will be sent to the LRD for through checking (for details refer to the Quality assurance)