Density is just a measure of how many people, or shops, or cars, or whatever you choose to measure is stacked on a given area. Architecture comes in, among other things, when you are able to reach certain levels of density while maintaining a degree of privacy which is compatible with what you expect in a given culture. As much as seeing cementerys says you something about what is the vision of a singular architecture in many european cities (you can sometimes make there what is not allowed in the ordinary city), seeing the courtyards tells you many things about how a culture deals with this privacy issue. This is Paris, the courtyard of a block by the Rue du Commerce (not far to the south from the Eiffel tower).