Paseo de la Cetellana is Madrid's principal north-south avenue, running for several miles through the heart of the city and bordering the Salamanca district to its west.
The primary north-south avenue in Madrid is the Paseo de la Cetellana. 
mnli hypothesis: The primary north-south avenue in Madrid is the Paseo de la Cetellana.  premise: Paseo de la Cetellana is Madrid's principal north-south avenue, running for several miles through the heart of the city and bordering the Salamanca district to its west.