Ken,
Probably the old British 1:63,360 sheet is the best map of the city in the early 20th century, though Rennell's map of Bengal in the 1700s will show it too.
plate 12 (of 13) is . Plan of the environs of the City of Dacca
A colour copy can be ordered from us for $16.50 paper/$45 digital,
http://catalogue.nla.gov.au/Record/6346859
or you could use the online version Gale digitised of the 1781 edition. Dacca is still plate 4.
<http://find.galegroup.com/mome/infomark.do?
I doubt there's anything earlier/more detailed than this.
Brendan Whyte
National Library of Australia