Bangkok
Start with the line you can walk to
Bangkok is a group of districts tied together by the BTS skytrain, the MRT subway, buses, taxis, and boats on the Chao Phraya and the canals. The official city name matters less, day to day, than whether you can reach a station without sitting in traffic first.
The BTS Sukhumvit Line runs east and north along Sukhumvit Road and Phahonyothin Road. The BTS Silom Line crosses the river and serves the older business districts around Silom and Sathorn. The MRT Blue Line makes a loop that includes Huai Khwang, Rama 9, Sukhumvit (where it meets the BTS at Asok) and Silom. The Airport Rail Link is a separate line to Suvarnabhumi Airport. Boats on the Chao Phraya are useful if you live or work near the river; they are not a substitute for the train in most inland districts.
People often start their search on Sukhumvit because the stations are close together and many condominiums were built within a short walk of a platform. That convenience has a cost, and the road itself is frequently jammed. Other parts of the city, such as Ratchada and Huai Khwang or the area around Ari and Chatuchak, trade a slightly longer trip to some offices for streets that feel less packed.
This guide does not rank districts. It describes how they connect. If you have school-age children, read the schools by area file before you sign anything, because several large campuses sit well to the east or outside the central districts.