Housing area- office area ratio for the lots in the Barrio de Salamanca and the surrounding areas
One of the main aims of urban planning in Europe since the 1980’s has been to avoid a destruction of the soul of the historical areas through the insertion of large scale offices. This is something that can be quite controversial, as in some areas it has led to no offices but no population either. In Madrid we can see a minute mix of uses. In many cases GIS would not return a value as it is a division by zero (and here I can hear residents of the area, as some lots have clearly a lot of offices, but the fact is that cadastral data considers them other uses). This is somehow as mixed as uses can get in Madrid.
metrhispanic 
Market Street in Philadelphia is almost entirely office space making it a desolate and scary place to walk after business hours. A mix of residential and office is essential to a safe and vibrant city.
… to which I agree. The problem is when you have places as Market Street (Azca in Madrid is also that kind of area) or when you have just square miles of housing with nothing else. Our cities are denser than yours, but some areas are just residential;albeit there is some retail (no offices, no other significant source of jobs), you can find hughe areas in which it really supports a very limited urban life.