Viewed from above, the main portion of the city resembles an airplane or a butterfly. The Monumental Axis goes east-west and holds government buildings and monuments. The other axis is curved in a north south direction. The city is commonly referred to as "Capital Federal", or simply "BSB". As the national capital, Brasília is the seat of all three branches of the Brazilian government. The city also hosts the headquarters of many Brazilian companies. Planning policies place residential buildings around expansive urban areas. The plan includes large avenues. It divides the city into sectors with different purposes, including accommodation and tourism. The city is built around an artificial lake, Lake Paranoá.