in the west to roughly the Eastern Metropolitan Bypass in the east—a span of . The north–south distance is greater, and its axis is used to section the city into North, Central, South and East Kolkata. North Kolkata is the oldest part of the city. Characterised by 19th-century architecture and narrow alleyways, it includes areas such as Jorasanko, Rajabazar, Maniktala, Ultadanga, Shyambazar, Shobhabazar, Bagbazar, Cossipore, Sinthee etc. The north suburban areas like Dum Dum, Baranagar, Belgharia, Sodepur, Khardaha, New Barrackpore, Madhyamgram, Barrackpore, Barasat etc. are also within the city of Kolkata (as a metropolitan structure). Central Kolkata hosts the central business district. It contains B. B. D. Bagh, formerly known as Dalhousie Square, and the Esplanade on its east; Rajiv Gandhi Sarani is on its west. The West Bengal Secretariat, General Post Office, Reserve Bank of India, Calcutta High Court, Lalbazar Police Headquarters and several other government and private offices are located there. Another business hub is the area south of Park Street, which comprises thoroughfares such as Jawahar Lal Nehru Road, Abanindra Nath Tagore Sarani, Dr. Martin Luther King Sarani, Dr. Upendra Nath Brahmachari Sarani, Shakespeare Sarani and Acharay Jagadish Chandra Basu Road. South Kolkata developed after India gained independence in 1947; it includes upscale neighbourhoods such as Bhawanipore, Alipore, Ballygunge, Kasba, Dhakuria, Santoshpur, Garia, Golf Green, Tollygunge, New Alipore, Behala, Barisha etc. The south suburban areas like Maheshtala, Budge Budge, Rajpur Sonarpur, Baruipur etc. are also within the city of Kolkata (as a metropolitan structure). The Maidan is a large open field in the heart of the city that has been called the "lungs of Kolkata" and accommodates sporting events and public meetings. The Victoria Memorial and Kolkata Race Course are located at the southern end of the Maidan. Among the other parks are Central Park in Bidhannagar and Millennium Park on Rajiv Gandhi Sarani, along the Hooghly River. Two planned townships in the greater Kolkata region are Bidhannagar, also known as Salt Lake City and located north-east of the city; and Rajarhat, also called New Town and located east of Bidhannagar. In the 2000s, Sector 5 in Bidhannagar developed into a business hub for information technology and telecommunication companies. Both Bidhannagar and New Town are situated outside the Kolkata Municipal Corporation limits, in their own municipalities. Climate Kolkata is subject to a tropical wet-and-dry climate that is designated Aw under the Köppen climate classification. According to a