Though there are varying borders for downtowns in the US and even vs its CBD (Central Business District) main one. Some are one and the same as the definition does claim for most, a downtown and CBD are the same.
Real Estate areas that are downtown housing areas can also have varying borders and their links give them cities maps. Refin is one that if you type in downtown of that city. It will give a highlighted border along with others.
The city of Chicago seems to be an outlier in it has a separate border given by the city for its CBD and Downtown by a law it has on its books.
https://blog.chicagocityscape.com/ch...e-8c2a88f3fe19
Also google maps gives some downtown border highlighted. For many it does and for Chicago it does not any more as it used to for downtown showing just its Loop area. Now it shows the region with no highlighted border.
These are some maps given by real estate sights.
Seattle - realtor.com
https://www.realtor.com/realestatean...le_WA/overview
Seattle - Redfin
https://www.redfin.com/neighborhood/...wntown-Seattle
Seattle - Homes.com (map is lower in the link)
https://www.homes.com/seattle-wa/nei...3deb2533dcb3a1
Chicago seems to have a more varied area of what is the downtown living region. Some may be what is zoned downtown where the sky is the limit minus the FAA and Nimby's and Alderman final decision.
Chicago - Neighbors.com (general map with neighborhoods mentioned)
https://www.neighborhoods.com/neighb...icago/downtown
Chicago - Apartment.com
https://www.apartments.com/downtown-chicago-chicago-il/
Chicago - Redfin (most unusual because it cuts downtown off at the Chicago river on the west, yet goes further south and north)
https://www.redfin.com/neighborhood/...4699:-87.70251
Canadian cities tend to do larger downtown area as Toronto is given as 6.4 Sq/Mi that is in general a largest downtown. In some cities we can do that and be fair, but that might be seen as the greater downtown.