North Karnataka was actually less productive region in Karnataka because it was ruled by Persian and Urdu rulers who concentrated less on the region's development another reason being it is one of the driest places in India and an arid and semi-arid landscape.
However nowadays - Gulbarga, Raichur, Hubballi Dharwad, Bagalkote, Bijapura, Bidar are moderately developed decent cities and are actually less polluted compared to Delhi, Hyderabad, Mumbai, Kolkata , Noida and other big cities.
Gulbarga is the largest city and economic capital of North Karnataka.
Raichur is known for Hatti Gold Fields inspite of Telugu population.
Gulbarga, Bijapura, Bagalkote and Hubballi also contribute atleast a small percentage towards economy of Karnataka state.
However Mandya is the largest city in Karnataka and the most developed city in Karnataka followed by Hassan and Davangere and Gulbarga.