Quick answer

Use Sultanahmet for the classic historic core, Galata/Karakoy/Beyoglu for mixed days and evenings, Kadikoy for food and markets, Uskudar for views, Balat for colorful streets, and Bosphorus districts for scenic slower time.

The useful area map

A practical Istanbul map starts with functions. Sultanahmet is the monument cluster. Galata, Karakoy, and Beyoglu form the flexible middle layer. Kadikoy adds markets, food, and nightlife on the Asian side. Uskudar is strong for views and ferry links.

Balat, Besiktas, Ortakoy, and Bosphorus villages are better as targeted half-day choices than default bases for every traveler.

Planning Choices

Historic core
Sultanahmet and Fatih. Best for first-day monuments.
Urban mix
Galata, Karakoy, Beyoglu. Good for walking, food, ferries, and evenings.
Asian side
Kadikoy and Uskudar. Food, markets, views, and ferry rhythm.