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Digital Cartographic standards for 1:50,000 Geologic map: some important considerations
These physiographic domains have distinctive geological evolutionary history. Again each of these physiographic domains has their inherent dissimilarities and complexity. For example, the Peninsular shield is a mosaic of four major cratonic domains- the Southern Indian Craton (SIC), the Central Indian Craton (CIC), the Eastern Indian Craton (EIC), and the western Indian Craton (WIC). These cratons have evolved from Archaean through Proterozoic, but their evolution is not exactly similar in the sense that, while the Archaean greenstone sequences are more widespread and prominent in the SIC, are not remarkable in the other three cratons. The linear to curvilinear Proterozoic fold belts that are identifiable in WIC (Delhi, Aravalli), CIC (Mahakoshal, Sakoli) and EIC (Singhbhum) are not identifiable in SIC. Similarly, the mildly deformed cover sequences, such as, Bijawar, Gwalior, and Abujmar sequences which are present in CIC, are rare in other three cratonic domains. Therefore, stratigraphic correlation and subsequent standardization of map units even within a single physiographic domain is a difficult job, leave alone the correlation between different physiographic domains. However, post Mid-Proterozoic, the evolutionary history of the Peninsular shield is more or less uniform, except for the fact that, the terrestrial facies covers of linear grabens (Gondwana) are present in all the cratonic domains barring the WIC.
The extrapeninsular belt comprises a huge volume of reworked shield elements, but due to the reworking during the Himalayan orogenesis, the original characters of these elements are so much obliterated that their correlation with their peninsular counterpart is yet to be achieved.
Constructing unified stratigraphic legends for each of the physiographic domains can be an optimal solution; if necessary the different cratonic domains can be treated separately also. These stratigraphic legends that represent a taxonomic type classification (having major-minor code system) can be used to formulate the hierarchical map unit symbols, or in other words a unified color and/or pattern code for all the Supergroups, Groups and Formations. Currently no such hierarchical symbolsets are in vogue in any of the GIS or CAD packages. It is imperative that this approach will demand creation of hundreds of symbols, which has to be significantly different from each other in order to distinguish nominal categories. Moreover, if lots of color are used for certain domains, the choice of color remaining available for the other domains will be much too limited for satisfactory discriminations.
Scale of original survey:
Field geologists tend to map geological features depending upon the scale of survey. What is definite at small scale may be only inferred at larger scale. The nature of the administrative boundary does not change with map scale; the cartographer only applies graphical generalization if at all necessary (large scale to small scale). It is commonly defined and observed with a resolution with much greater precision than it is plotted. Geologic objects are commonly defined and observed with a resolution that is near the intrinsic resolution of the map (Haugerud, 1998). Symbols (continuous or dashed lines) are used to denote whether an object is located as well as or more poorly than can be depicted at that scale.
Geologic data models should be consistent enough so that any geologic feature may be represented as one or more geometric shapes (volumes, surfaces, areas, lines) depending on the type and scale of the map. For example, rock units are not confined to a volume (in 3D geometry) or area (in 2D geometry). At a smaller scale, thin rock units may appear as surfaces (represented as lines or line segments in two dimensions) and small, but significant units may be represented as points. Similarly, veins, dikes, fault zones, etc. may change representational geometry with changes in scale. In the present case the scale of systematic mapping and scale of map presentation is same (1:50,000), so if the consistency of original surveying, and the data model is maintained then map compilation and presentation will prove to be an easier task.
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