Sigil was located in the Outlands, hovering above the immensely tall landmark known as the Spire that stood at the plane's center. From the Outlands, it was possible to see Sigil hovering atop the Spire as the mountaintop vanished into nothingness.
This city has more political intrigue than Waterdeep, the people are more arrogant than Westgate merchants, and the air's more foul than a Zhentil Keep sewer.
— Joel of Finder
Sigil was shaped like the inside of a torus. According to official measurements by the Harmonium, the city's primary diameter―that is, the ring's diameter―was 5 miles (8 kilometers), with a circumference of 20 miles (32 kilometers). Later measurements put the primary diameter at approximately 6.4 miles (10 kilometers), with the same circumference as the Harmonium's measurements, and a secondary diameter―the ring's thickness―of approximately 1.5 miles (2.4 kilometers). Despite these attempts at measurement, the city did not have a fixed size and its dimensions could be changed at will by the Lady of Pain.
Sigil was divided into six wards. Although the boundary between wards was not clearly marked on the city's streets or maps, it was usually easy to identify a ward based on the general upkeep and packing of the buildings, as well as the type of business conducted there. Counter-clockwise around the ring, the wards of Sigil were the following:
