Revised Gravity Maps of India (2006 series) – A Cartographic Perspective
R.M. Sundaram
Geologist(Sr.)
Geological Survey of India,
Email: rmsundaram2006@gmail.com
Geological Survey of India (GSI), National Geophysical Research Institute (NGRI), Oil and Natural Gas Commission Limited (ONGC), Survey of India (SOI) and Oil India Limited (OIL) have jointly taken up a collaborative project to revise the Gravity Map India (1:5,000,000) published in 1975. Basic gravity data collected over 143,786 stations by these organizations during the last two decades was synthesized for generation of Revised Gravity Map Series. Map Printing Division, Geological Survey of India, which has the state of art facilities in GIS and Digital Cartography, has been entrusted with the digital processing and final publication of Revised Gravity Maps of India (2006 series). The series comprises Free-air Gravity Map of India (1:2M), Bouguer Gravity Map of India (1:2M), Bouguer Gravity superposed over Geological Map of India (1:2M) and Gravity Image Map of India (1:5M).
The gravity anomaly contour data (both Free-air and Terrain-corrected Bouguer) in the DXF format, terrain-corrected Bouguer data as a perspective TIFF image and gravity station distributions as x, y ASCII data were the main inputs for digital cartographic processing and subsequent publication of these maps. Gravity anomaly contour, gravity image and station distribution data has been converted into geospatial format on Lambert Conformal Conic (LCC) projection by employing Intergraph’s MGE suite and ESRI’s ArcGIS applications and has been combined with the existing geospatial data (point, line and polygon) such as geology, drainage, transportation network, administrative boundaries, bathymetry etc. The various contour intervals have been suitably depicted with appropriate symbolization styles for Free-air and Bouguer gravity maps. Representation of the Bouguer gravity contour data over geology polygon data from published Geological Map of India (1998) is a challenging task and has been accomplished keeping in view of the importance and potential of this map for the utility of the geoscientists at large. The terrain-corrected Bouguer gravity perspective image was generated by interpolating the point-anomaly data through GeoSoft application at a resolution of 800 DPI. The cartographic designing process adopted for on-screen visualization and paper printing of all these maps especially Gravity Image Map of India is significant for its quality reproduction within a shortest period