I'm writing this post as a quick response to a Chicago Genealogy Facebook page question about how to use an address to determine a 1920 Census ED using the maps found on alookatcook.com.
1) Find the address using Google Maps. I'm going to try 2711 Hillock.
2) Once you've found the address, note the large cross streets. In this case, the canal/river is prominent and I notice that the address is southwest of the curve.
3) Go to alookatcook.com and click on the 1920 Ward map.
4) Notice how prominent the canal is. Based on the Google map, I guess that the address is part or the 4th ward so I click on the number 4 to see the map of EDs within the ward.
5) Going back to the Google map, I look for large streets and try to find them on the ED map.
I see that the address is west of Halsted and south of Cermak. Does that help?
Yes. I see Halsted on the ED map so that narrows down the eastern border.
6) I go back to the Google map and look for other streets close to the address. I see names like Throop, Grove, Loomis, Lock, Poplar.
7) I go back to the ED map and try to find those streets.
I see that Throop and Loomis are boundaries for some EDs and I notice that the river, Archer, Lyman, and 31st are the north/south boundaries.
8) I go back to the Google map to find the Archer, Lyman, etc. and finally I'm able to say that my address looks like it's south of the river and north of Archiver between Throop and Loomis.
9) ED 218 is a good guess so from there, I go to Ancestry.com (or another site with the census) and scroll through looking for the Hillock address. Most times when I do that I refer back to the map(s), and I can often tell the path that the enumerator was taking. It can help me to guess whether I need to look at the beginning, middle, or end of the image set.
Hope that helps! It's not an easy process--lots of trial and error--but it does work.