Rennell's Atlas one of the earliest atlases of Bengal and its adjoining areas. To facilitate commercial navigation, the East India Company's surveyor and engineer james rennell was assigned to conduct a survey of the Bengal river system and prepare their maps. From 1763 to 1773, Rennell compiled a set of maps of Bengal for the British Government. His Bengal Atlas, published in 1779, was a work of the highest importance from commercial, military and administrative points of view. To all users- academic, administrative and navigational, Rennell's Atlas was the dependable guide until professional maps were made available in mid 19th century.
Overlays of the Rennell's map with the modern one give an interesting picture of the diversified nature of the river courses of this region. It shows considerable differences between the courses of the present-day rivers and those of Rennell's time. The ganges and the jamuna had different courses in the bengal delta of that time. It is demonstrated that the brahmaputra was running along a course now occupied by the old brahmaputra. The tista, which was flowing directly south and branched into many streams, all of which then fell into the Ganges, is now joined with the northern part of the Jamuna. The karatoya, in Rennell's time, was flowing past Bogra and discharged itself into the Brahmaputra. But now, it follows the channel of the bangali more directly, and meets the Brahmaputra upstream. In Rennell's map the junction of the meghna and the Ganges was shown at south Lakshmipur but today it is near Chandpur.
In 1956, JP Morgan and WG McIntire carried out extensive work on the Quaternary Geology of the bengal basin and showed that the diversified nature of the river courses was directly associated with the recent differential upliftment and subsidence of the area. The Tista changed its course in the flood of 1787 and consequent upon the earthquake of the same time, this change could have been accompanied by renewed uplift and tilting of the barind tract. The diversion of the Brahmaputra occurred due to the compensatory uplift of the Barind and the madhupur tract, and that compensatory uplift had occurred due to the sinking of the zone between those tracts. Some believe this change occurred between 1720 and 1830. After development of the present course of the Jamuna, the gorai attained its present course, so that the water of the Ganges could easily discharge into the bay of bengal. The changing of the course of the Ganges and its tributaries and distributaries is related to the development and evolution of the bengal delta.
In a word, Rennell's map is a compendium of the river course history of the Bengal delta and its geomorphological changes as well. [Sifatul Quader Chowdhury and Monirul Hoque]