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Digital Cartographic standards for 1:50,000 Geologic map: some important considerations
Basemap content:
Representing relief information is of utmost importance in geologic maps, but has to be done without compromising clarity. The purpose of using basemaps in thematic mapping is mainly to provide locational information and to some extent explanation for the thematic features observed. Geologic data are recorded and presented on a base, most commonly a topographic map. It is very important to represent relief in the base map and the most effective method of representation is by topographic contour lines (Maltman, 1998; Spencer, 1993). It is easy to construct topographic profile from contour lines (which is necessary for constructing a cross-section). An experienced map-reader can also gain idea about the attitude and disposition of rock units from the relationship between the contour lines and the contacts of different rock bodies. Drainage is also used, as it tends to follow the fracture pattern in the rock bodies. Next to contour lines, also roads and towns are used as base map features (for location).
GSI has decided to use triangulation points, spot heights, motorable roads, highways, drainage, important localities and administrative boundaries as the supportive basemap content. Contour lines though of prime importance will be omitted because of restrictive government policies. Thus decided the symbols for representing these basemap features can be generated in such a way such that they do not obscure the primary content of the map.
Presentation of structural features:
A geological map not only exhibit the spatial distribution of rock units in three dimension but also reflects a wide spectrum of earth science database, in which the most significant element is the meso and the megascopic structural feature. These features can be broadly grouped into primary and secondary type, which play vital role in the following studies.
- Environment of deposition as well as syndepositional tectono-magmatic episode
- Stratigraphic and tectonic order of superposition
- Reconstruction of tectonic history and postulation of regional framework
- Delineation of economically potential zone and hazard prone areas
All these studies are carried out to formulate a near factual model for which the standardized database has to be the basic premise to start with.
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