Babylonian clay tablet that has been generally accepted as "the earliest known map" is the artifact unearthed in 1930 at the excavated ruined city of Ga-Sur. The surface of the tablet is inscribed with a map of a district bounded by two ranges of hills and bisected by a water-course. This particular tablet is drawn with cuneiform characters and stylized symbols impressed, or scratched, on the clay. Inscriptions identify some features and places. In the center the area of a plot of land is specified as 354 iku (about 13 acres), and its owner is named Azala. The map is identified as of a region near present-day Yorghan Tepe (Ga-Sur at the time), although the exact location is still unknown. The geographic content consists of the area of a river valley which may be that of the Euphrates flowing through a three-lobed delta and into a lake or sea in the northern part of Mesopotamia. Also shown on this tablet may be the tributary river the Wadi-Harran, the Zargos Mountains in the east, the Lebanon, or Anti-Lebanon in the west, and cities which are symbolized by circles. North, East and West are indicated by inscribed circles, implying that maps were aligned in the cardinal directions then as they are now. This tablet also illustrates the sexagesimal system of mathematical cartography developed by the Babylonians and represents the earliest known example of a topographic map.