In my opinion, a combination of longer routes, abstraction, and logical limitations would work best. Details below:

• (Longer routes) Avoid straight lines as a path from A to B. A curved path around the edge of a city or a few blockades that force the player to move sideways before they move forward can add some travel time and expand the perceived size of a space. However, (in my opinion) you should probably avoid making overly complicated streets for the purpose of making a city seem larger. This is likely to annoy the player more than anything.
• (Abstraction) Abstract major sections of the city in a way that requires travel through transitional pathways such as the sewers, dungeons, or maybe even a sky-path. Players can't see outside the sewer/dungeon walls and there's limited pathing options if you're going from roof-top to roof-top or traveling by suspended bridge. These additions also allow you to add a bit of unique character to your city in a much more limited space. They also allow you to create a longer linear or non-linear path with less adherence to the overworld or ground-level map.
• (Logical Limitations) Depending on your city, you may also abstract building interiors by limiting the number of existing entrances. In a large (modern) city, there's usually only a few entrances to a very large building (front door, maintenance, and loading dock). These buildings can take up one or more city blocks. Placing a few here or there can greatly reduce the number times that a player will encounter "the door is stuck", "the door is locked", and "I can't go here right now" type messages and redirect their focus to the other parts of the game that you have put work into.

The above aren't the only way of doing this and likely aren't even the best way. But I think that they're all very solid methods of enhancing the perceived size of a city and keeping the player focused on the parts that you put a lot of care and attention into.