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The Magh ( Mog ) is the term used in history of Bengali and others people of South Asia for the Marma and Arakanese/Rakhine of Arakan. During the 16th and 17th centuries, the Mrauk U Kingdom of Arakan expanded its territories to the Chittagong area of Bengal. The navy of the kingdom of Arakan or rather Magh sailors along with the Portuguese had plundered along the coast of Chittagong; as well as in the rivers of Bengal; and captured many Bengalis and sold them in the slave markets that were run by the Dutch East India Company, VOC in Batavia. For those notorious activities in the past, the Arakanese were called Magh pirates by the people of Bengal. Another alternative suggestion for the term Mog suggests that the word is derived from Mongol. That country is mentioned in the Arakanese Chronicles as the original residing place of the ancestors of the Arakanese kings who were the relatives of the Buddha.

During the hey days of the Arakanese kingdom, many Arakanese people who were called as Mogs lived in Chittagong region of Bengal. As Chittagong, what is now in Bangladesh, was part of Arakan in the past, the Arakanese Magh governors ruled part of Bengal by residing in that city as the capital of the colonial region of Arakan. 

Sandwip Island, island situated in the Meghna River estuary, southeastern Bangladesh. It is the easternmost island of the Padma River (Ganges [Ganga] River) delta. It is about 25 miles (40 km) long and 3–9 miles (5–15 km) wide and is separated from the Chittagong region to the east by the Sandwip Channel, one of the four mouths of the Meghna estuary, and from the Hatia Islands to the west by the Hatia River. Formed of silt deposits from the Meghna, it is an exceptionally fertile area. It is, however, continually subject to destructive ocean waves. 

Sandwip Island was a 17th-century stronghold of Portuguese and Arakanese (from Myanmar [Burma]) pirates until the Muslim governor of Bengal put an end to their depredations in 1665. It remained an administrative problem under early British rule. The island is connected to the mainland by boat.

https://www.britannica.com/place/Sandwip-Island

https://en.wikipedia.org/wiki/Sandwip

The Renell map has a coordinate system that shows longitude east of Calcutta. The prime meridian (the line of longitude that is defined as 0°) on this map passes through Calcutta, which was then the capital of British India. The reference point for the Calcutta Meridian was the old Fort William in Calcutta, India. Its longitude was determined to be 88° 22′ 30″ E by the British surveyor James Rennell in the late 18th century. In modern coordinates, the location of Fort William is approximately 22.5594° N, 88.3418° E.

The use of a coordinate system, including longitude and latitude, was a major advancement in cartography and surveying during the 18th century. It allowed for greater accuracy in map-making and navigation, as well as improved communication and understanding of geographical locations.

During the time period when the Renell map was created, there was not yet a universal standard for measuring longitude. Different countries and organizations had their own systems, and the British East India Company used their own system which was based on the meridian of Calcutta, rather than the meridian of Greenwich. This was likely due to practical reasons, such as the fact that it was easier for the British surveyors to use local observations and instruments to determine longitude relative to a nearby location rather than a distant one. It wasn't until the late 19th century that an international conference established the Prime Meridian at Greenwich as the standard for measuring longitude.

James Rennell (1742-1830) was a British geographer, surveyor, and cartographer. He is widely regarded as one of the most important figures in the history of cartography and is known for his contributions to the science of geography, especially in the fields of oceanography, hydrography, and topography.

Rennell served in the British East India Company's navy for several years and was instrumental in the surveying of the coast of Bengal, which led to the publication of his landmark work "Memoir of a Map of Hindoostan" in 1783. He was appointed surveyor-general of Bengal in 1767, a position he held for over 20 years, during which time he conducted extensive surveys of the region and produced numerous maps and charts.

Rennell's maps and atlases were highly regarded for their accuracy and detail, and his work had a significant impact on the development of cartography and geography in the 18th and 19th centuries. He was elected a fellow of the Royal Society in 1781 and received numerous other honors and awards throughout his lifetime.

The map titled "A Map of Hindoostan or the Mogul Empire" is a larger-scale map that covers a wider geographic area than the Bengal and Bahar map. It was also created by James Rennell, and published in 1788. The map of Bengal and Bahar is actually a portion of this larger map, focusing specifically on the regions of Bengal and Bihar.

The "Map of Hindoostan or the Mogul Empire" is notable for being one of the most accurate and comprehensive maps of India at the time of its publication. It was based on extensive survey work and drew on a variety of sources, including previous maps, travel accounts, and astronomical observations. The map also included important geographic features such as rivers, mountains, and major cities, as well as political boundaries and information on local customs and religions.

Overall, both the Bengal and Bahar map and the Map of Hindoostan or the Mogul Empire were important contributions to the field of mapmaking and surveying in India during the late 18th century. They provided valuable information on the geography and political organization of these regions, and helped to further the British East India Company's knowledge and understanding of the subcontinent.

Full atlas 

Memoir of a map of Hindoostan or the Mogul Empire (Flipbook)