Observation is particularly important where there is no permanent record of activities –discrete observation can reveal whether there is improper access to a restricted area.

对于没有持续性记录的活动来说，实地观察法是一种非常有效的方法。持续的观察可以发现是否有不正确进入受限制区域的行为。

youdao

Large numbers of riot police ringed the area and restricted access to the court from dawn.

ECONOMIST: Malaysia

The Postberg area of the park is opened especially for viewing the fields of flowers, with a restricted number of vehicles allowed access.

BBC: South Africa's Western Cape: The secret coast