Narrow buildings -- these buildings were taxed based on the number of linear feet facing the canal. In the picture, the door in the middle is the door for a house that is only as wide as that door, "the skinniest house in the world".
Covered / Bricked over windows -- buildings were taxed based on the number of windows. Building owners could save money simply by bricking over some windows.
"In the early 17th century, buildings were taxed by the number of floors leading up to the cornice of the roof.
Architect François Mansart ingeniously responded to this rule by hiding an additional story or two under the roof for additional living space, rendering it exempt from taxation."
...and hence the "distinctive architecture of Paris, with its mansard roofs".
You have to read the article, not just look at the pictures.
Umm, RTFA
The British taxed based on a count of windows.
Evidently not...