An abandoned site or region may have been populated or visited by humans in the recent past; in terms of survival, this implies that in such places would be possible to find some additional resources.
It is a common assumption to think that once civilisation reaches a place there is no turning back; it is true that many times it happens that way, but there are some exceptions, and this could be important under survival circumstances. Towns and human installations appear in all place for good reasons, and if those reasons disappear or it is found that somehow, it is a bad business to stay, people will emigrate. The typical "ghost town" exists even in countries with high population density and, as is the case of Spain, but in all cases something is to be gained if you are in a dire stuation.
People can choose to live in a city, water sources might have been exhausted, other natural resources that led to the colonization of this site might have been depleted, or environmental conditions could become too dangerous or unfeasible to sustain life, as it happened in places like ancient Pompeii, in Montserrat and Chaitén.
Reasons to abandon towns are plentiful and the survivor who suddenly find a site with such features should not assume that he or she has reached back civilization; instead, it should be assumed that a survivor under such circumstances might have found some bonus resources, albeit with some caveats: For some reason people have gone, and it should be assumed that the reasons to leave were good ones. If they had time to leave, they will have had dismantled and taken most things of any value and if not, gradual attrition due to environmental factors and the more or less casual looters that usually take advantage of such situations would have done the rest of the disappearing act. Do not underestimate what you can get in a ghost town, but don't overestimate thing either.
TThe remains of an abandoned and dismantled railway track.
It is especially important to keep in mind that albeit civilization was there, it is no more; this means that in most cases, there will be no rescue and no visitors, since the town has been abandoned. You will notice soon enough if there has been human presence after the place was deserted. A survivor in a ghost town should assume that he or she is now somewhere in-between pure outdoor and urban survival.
Abandoned installations near roads or railways might be an exception for the good: often, railway companies close some stations that are not profitable, but trains keep passing there. Check the state of the railway tracks - if they still exist - to see if trains still go following some schedule; the same could be applied to roadside buildings like abandoned gas stations, hotels, etc.
In the case of airstrips and abandoned harbor installations, however, signs of recent usage might indicate danger: flying aircraft is an exercise that requires more planning than driving a car thorough a road, and so, before every flight pilots inform themselves about the state of aerodromes and airports along the routes that they follow. They will not risk landing in abandoned airstrips unless they are in a dire emergency or they are part of some sort of smuggling scheme. So, if you notice some activity in an abandoned airstrip or harbor, be careful, especially if the activity takes place at unusual hours or in bad weather.
In the case of towns or installations abandoned in a war zone, be especially careful: If combat operations are ongoing you should assume that the place will be visited sooner or later by regular or irregular forces; that could mean rescue or capture for you. Also, be very careful with landmines, unexploded ordnance and booby traps.