It is often difficult to grasp. This is why when you look at an empty piece of land, it can sometimes be difficult to visualize actually fitting a building on it. And why when you look at an empty room, it's common to think, "there's no way that furniture will fit in here." But in the end, it does fit.

It also tends to be relative. Here in North America, it is common to argue over things like parking space dimensions and drive aisle widths. We'll say things like, "well, people like their big cars." But then you travel to Europe and you find streets like this:

And this:

The first is only marginally bigger than the width of a parking space in Toronto (2.6 meters). And the latter is only marginally bigger than the width of a typical two-way drive aisle (6 meters). So are these too small? Well, it depends on your perspective.

If your basis of measurement is the size of cars, then these streets will seem too small. Cars also keep getting bigger, so you have this inflation factor to deal with. But if your basis of measurement is something else, such as walkability, then maybe they're just right.

It's hard to think of Barcelona and not think of its famed street, La Rambla. But this same street design (and name) also appears in other cities throughout Spain. The above two streets are in Palma. The first is also called La Rambla (which is supposedly derived from an old Arabic word meaning sandy riverbed) and the second is called the Paseo del Borne. Both follow the exact same urban design principles. They're broad tree-lined streets with a large center median dedicated to only pedestrians. All car traffic is relegated to the sides. What's great about this design is the following. One, it reallocates public space according to who uses it the most (i.e. pedestrians). Two, it consolidates the main pedestrian realm (in lieu of just having larger sidewalks on either side of the street). And three, it establishes a clear hierarchy for the street. Pedestrians are most important here, and that's why they get the center position. It's surprising that more cities don't adopt this same design.