It's not really accurate to think of a "main" route when discussing the silk roads. Different goods were transported by different routes, depending on the locations of markets and local conditions.

But yes, the chang'an<->gansu corridor<->Fergana valley is often called a principal overland route. Many of the caravans that went south of the pamirs would rejoin in Merv, while the maritime routes would often rejoin in a Mediterranean port like Tyre (during the roman period) or cities like Basra in the medieval period.

Just keep in mind that this map (and any other depiction) of the silk roads is necessarily incomplete. This map omits important areas like Kashmir because the authors simply haven't visited. Depicting the thousands of known sites is overwhelming, and the connections between them were often intermittent.