I'm not sure why you want such a map. One can be found on the National Archives film series A3378. I actually have a scan of it on my hard drive. I don't think there is online that map however. Or....
1. Ancestry has a description of the census districts. If you go to their Census section, choose 1920, and then scroll down the initial search page past the name entry box..you will see their geographical section...and if you choose New York (state) and then New York (county)...you would see within the wards descriptions of the census districts...and if you were looking for a block to get the ED #, then you could find it on that site.
2. However, why bother..when you can use our utilities at stevemorse.org ? What you would do is go to our census section, choose the ED finder..... accept the default of 1930....find your address (or at least the two streets that make up a corner of your target block)....get the ED #(s), and then translate that 1930 ED # with our appropriate utility (shown as a button on the 1930 utility) to the corresponding 1920 ED #.