Well, if i would have to explain it::
Features and terrain:: have to be in the fat cross (or later in the expandable work radius) regardless of borders or connected to the trade network (e.g. natural wonder, hill, mountain, grassland, bamboo, volcano etc).
Bonuses: have to be inside your cultural borders and fat cross (or 3 tiles after expansion) of the city, must be connected to the trade network and need the appropriate improvement.