Giza is the third largest city in Egypt. It is located on the west bank of the Nile River, some 20 km southwest of central Cairo. Along with Shubra El-Kheima, Cairo and Helwan, the four cities form the Province of Greater Cairo metropolis. The city of Giza is the capital of the Giza Governorate, and is located near the northeast border of this governorate in coordinates. It is located right on the banks of the River Nile. The city's population was 2,681,863 in the 2006 national census, while the governorate had 6,272,571 at the same census. Giza is most famous as the location of the Giza Plateau: the site of some of the most impressive ancient monuments in the world, including a complex of ancient Egyptian royal mortuary and sacred structures, including the Great Sphinx, the Great Pyramid of Giza, and a number of other large pyramids and temples. The plateau and its monuments have been recorded in the Giza Plateau Mapping Project run by Ancient Egypt Research Associates, directed by Dr. Mark Lehner. AERA's 2009 field season was recorded in a blog. The Great Pyramid of Giza at one time was advocated (1884) as the location for the Prime Meridian, a reference point used for determining a base longitude.