The use of land in Shanghai is organized in concentric rings, the core, first ring, second ring, and the third ring. The core is a primarily urban zone that constitutes 4.42% of Shanghai covering 280 square km. It is comprised of the following districts: Huangpu, Nanshi, Luwan, Xuhui, Changning, Jingan, Putuo, Zhabei, Hongkou, and Yangpu. The first ring measures 1,776.93 km and is known as the suburban vegetable circle. The second ring is 4,283.92 km and is used mainly for growing grain crops and other non-staple foods. The third ring is made up of mostly fishponds and orchards. Within the concentric rings there is a radiating pattern from the core with people unfailing along the arterial roads and waterways(click here for a map of urban growth). In addition, there is a trend of people from the core moving to the suburban zones while people from periphery are moving to the core. One of biggest problems Shanghai is facing today is the land use within its core. Its commercial land use within its core is ten percent less than developed countries and warehouse/industrial use is ten percent higher. In addition to this the land used for industrial use are often occupied by small factories who can't not expand because the lack of land. So, most of these factories have to truck in supplies and truck out the finished products to the suburbs. Furthermore this mixed use of land with factories, housing, and other commercial uses all combined together has led to high levels of population in the core.(Click here for suggested improvements)