Elturel is roughly 200-250 miles East of Baldur's Gate, since the Tieflings are fleeing persecution in Elturel following the events of the Descent into Avernus adventure, the starting area is likely somewhere between the two cities along the banks of the Chionthar river.
Baldur's Gate itself is a large, cosmopolitan port city and so is likely to be diverse and multicultural with peoples of varying races and ethnicities. This diversity will spread throughout the surrounding area as people naturally move around.
