Answer:
James Rennell was an expert in marine survey and hydrography, but now he was to conduct land survey and produce maps. How was he to go about it? Fortunately for him Abul Fazl's Ain-e-Akbari, had just been translated. Prepared in the reign of Akbar, it contained a thorough description of the empire and its administrative and revenue units known as subahs, sarkars, parganas, chaklas etc. But their boundaries were not precisely demarcated nor were other prominent geographical features, like rivers and mountains, graphically represented in a map or chart. Distances and areas were estimated roughly and not after accurate measurements according to scientific principles of map making.
these factors helped Renell to prepare indias maps