Yes, that is the Greenwich Meridian.
The Mississippi River was the natural boundary of the Louisiana Purchase on the east.
The Cascade Mountain Range divides eastern and western Washington. This natural boundary influences the climate, landscape, and vegetation of each region, with the west being more temperate and rainy and the east being drier and more arid.
The Mississippi River is the East boundary for Arkansas.
One natural feature that divides northern and southern China is the Qinling Mountains. These mountains run east to west, separating the two regions and influencing their climates and ecosystems. Additionally, the Huai River is often considered as a rough boundary between northern and southern China due to the differing economic and cultural characteristics on either side.
The Rio Grande
The spreading of plates from a divergent boundary that divides an existing landmass into two separate plates.
Egypt's natural boundary to the east is the Red Sea and Suez Canal. To the south and west there are no natural boundaries and it is often impossible to say if you are in Egypt or Libya.
Western Hemisphere, since the USA is West of the Prime Meridian through Greenwich, UK which divides the west half of our planet from the East half.
Convergent plate boundary.
The river that separates the east and west U.S. is usually considered the Mississippi.
The Mississippi River divides the US into East and West parts.
The East African Rift Valley was formed at this divergent boundary, located near the Horn of Africa.