The view is along the Riva Degli Schiavoni looking west towards the San Marco and the campanile (the tower at the right) as well as Santa Maria della Salute (the domed building towards the left). The entrance to the Grand Canal is between these two structures. 

In the painting, at the right, you can see the bridges which cross the various canals that lead into the lagoon. To me, it appears that Sargent is painting this from a rooftop of a church that is located (on the map) right above the letters "Sc" of "Schiavoni" (but I can't make out the name of the church). 

From Philip Resheph 
Date: 10/6/00 
The Riva Riva Degli Schiavoni runs from the Molo in front of the Palazzo Ducale  east . . . towards the Arsenale. . . .  Schiavoni means Slavs, and was where the trade from the Black Sea was carried out - it has always been very important. 

Notes: 

Exhibitions 

Sargent in Italy, 2002-2003 
 

• See Overview of Venice
• Venetian Studies
• See the year in review  1880