Depending on the purpose of the premise or area, it can be classified as either Yin or Yang. A human tenanted house, for example, is classified as Yang while a gravesite is classified as Yin. In Feng Shui the house of the living (yang) should be separated from the house of the dead (yin).
So do your absolute best, not to buy or rent a house that is located very near a gravesite!
In addition to gravesites, other premises such a hospital, funeral homes or places of worships are considered to be a bit on the Yin side. Try to stay away from them. If you cannot, then make sure that your main door do not face them.
Too Yang is not good either. Premises such as prison complexes, police stations, power generation plant, petroleum refineries fall into this category. The general rule is to stay a safe distance away from them.
Other sites to avoid include landfills, rubbish dumps, airports, military camps, and oxidation ponds.
Beware too, of high tension power lines and microwave transmitting stations. The emit electromagnetic waves which are believe to the cause of some ailments.
Avoid houses located on hilltops. Such locations are exposed to the elements and valuable Qi is dispersed. Moreover constant exposure strong cold or hot wind can affect your health.
Avoid very low lying areas too. Aside from the possibility of flooding, Qi is more likely to stagnate.
(Feng Shui House Location Trivial: Find a place with plenty of lively qi!)