INVESTIGATIONS OF THE DIMENSIONAL STABILITY OF SOME SELECTED MAP BASES

Abstract

Numerous types of map bases are available in the market. The cost varies considerably. Among other factors dimensional stability also varies. The dimensional stability is the property of a material to hold its form and size: 'in order that the accuracy achieved in the field survey or plotting by aerial photographs is preserved, the dimensional stability of material is of prime importance. Recently introduced plastic sheets like Astrolon and Astrofoil have superseded the advantages claimed by film and glass in respect of dimensional stability. In the interest of economy, a proper balance between the cost *nd quality of map bases has to be struck. Very little data othe than what the manufacturers have published is available$ hence the iecessity for well planned and controlled investigation in this direction. The problem assumes yet greater importance in India where the ranges of temperature and humidity are large enough to cause serious concern to the cartographer. Although a complete investigation requires an attack on numerous facets, the present one has been limited to the effects of temperature and relative humidity in the ranges which generally occur at Roorkee. On account of shortage of time and the absence of a suitable Air conditioning appliance, work has been further limited to the following ranges: