One of the many singularities of Venice is its toponymy. The city is in fact divided into six areas called the Sestieri and the numbering of the houses is not by street but by sestiere, so the address would be for example Cannaregio 3027 or Dorsoduro 2451. This subdivision is very old and even dates back, according to Tommaso Temanza to the time of Dogado Vitale Michiel II, in the year 1169 probably for tax and administrative purposes.

The Sestieri

The named Sestieri (known as Confinia ), which originally comprised about seventy Contrade with their respective churches, were divided into Sestieri di Citra (to the left of the Grand Canal from St. Mark's Square) and Sestieri di Ultra , (to the right of the Grand Canal).

The Sestieri di Citra  are:

• Castello
• San Marco
• Cannaregio

The Sestieri di Ultra  are:

• Dorsoduro
• San Polo 
• Santa Croce

Castello

It was formerly one of the major islands on which Venice was built and was given this name either because the first inhabitants found the ruins of an ancient castle built by Antenore there or because of the castle that was built to defend the Rhaetian islands.

San Marco

In ancient times, it was called Morso, perhaps because its soil was harder than that surrounding it, and Brolo because it was grassy and surrounded by trees. When the body of St Mark was transported from Alexandria and foundations were laid to build a basilica in his honour, the square became St Mark's Square.

Cannaregio

Named so because, according to some, it is a corruption of Canal Regio, a title given because of the width of the canal; according to others, and perhaps more justifiably, the name derives from Cannarecium and thus Cannaregio from the many reed beds found there.

Dorsoduro

It was so called because its soil rose above the surrounding area in the shape of a back, and was at the same time very hard and firm; but in some chronicles it is also called Dossoduro, from which some derive its name from the Dosduri  family that lived there.

S. Polo

From the name of the Church of St Paul, vulgarly S. Polo, built by Doges Pietro and Giovanni Tradonico in 837.

Santa Croce

It derives from the name of the Church of S. Croce that the inhabitants, who fled the invasion of the Lombards and took refuge on these small islands, erected.

The article I Sestieri: Venice's special features comes from Venice City Tours - Blog .